[bug] about:blank crashes on MacOS

[bryanlarsen]

Describe the bug

Setting up a webview with "about:blank" crashes Tauri on MacOS.

Reproduction

            let window_builder = tauri::WebviewWindow::builder(
                app,
                "main",
                tauri::WebviewUrl::App("about:blank"),
            );

Expected behavior

Expected a blank window, not a crash

Full tauri info output

[✔] Environment
    - OS: Mac OS 14.3.1 X64
    ✔ Xcode Command Line Tools: installed
    ✔ rustc: 1.77.1 (7cf61ebde 2024-03-27)
    ✔ cargo: 1.77.1 (e52e36006 2024-03-26)
    ✔ rustup: 1.26.0 (5af9b9484 2023-04-05)
    ✔ Rust toolchain: 1.77.1-aarch64-apple-darwin (environment override by RUSTUP_TOOLCHAIN)
    - node: 21.6.2
    - yarn: 1.22.21
    - npm: 10.2.4

[-] Packages
    - tauri [RUST]: 2.0.0-beta.16
    - tauri-build [RUST]: 2.0.0-beta.13
    - wry [RUST]: 0.39.0
    - tao [RUST]: 0.27.0
    - tauri-cli [RUST]: 2.0.0-beta.2
    - @tauri-apps/api : not installed!
    - @tauri-apps/cli [NPM]: 2.0.0-beta.2

[-] App
    - build-type: bundle
    - CSP: unset
    - frontendDist: ui

### Stack trace

```text
thread 'main' panicked at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-2.0.0-beta.16/src/manager/webview.rs:253:27:
called `Option::unwrap()` on a `None` value
stack backtrace:
   0: rust_begin_unwind
             at /rustc/7cf61ebde7b22796c69757901dd346d0fe70bd97/library/std/src/panicking.rs:647:5
   1: core::panicking::panic_fmt
             at /rustc/7cf61ebde7b22796c69757901dd346d0fe70bd97/library/core/src/panicking.rs:72:14
   2: core::panicking::panic
             at /rustc/7cf61ebde7b22796c69757901dd346d0fe70bd97/library/core/src/panicking.rs:144:5
   3: core::option::unwrap_failed
             at /rustc/7cf61ebde7b22796c69757901dd346d0fe70bd97/library/core/src/option.rs:1978:5
   4: core::option::Option<T>::unwrap
             at /rustc/7cf61ebde7b22796c69757901dd346d0fe70bd97/library/core/src/option.rs:931:21
   5: tauri::manager::webview::WebviewManager<R>::prepare_pending_webview
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-2.0.0-beta.16/src/manager/webview.rs:253:9
   6: tauri::manager::webview::WebviewManager<R>::prepare_webview
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-2.0.0-beta.16/src/manager/webview.rs:508:15
   7: tauri::webview::WebviewBuilder<R>::into_pending_webview
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-2.0.0-beta.16/src/webview/mod.rs:582:5
   8: tauri::window::WindowBuilder<R,M>::with_webview_internal
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-2.0.0-beta.16/src/window/mod.rs:354:7
   9: tauri::window::WindowBuilder<R,M>::with_webview
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-2.0.0-beta.16/src/window/mod.rs:344:5
  10: tauri::webview::webview_window::WebviewWindowBuilder<R,M>::build
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-2.0.0-beta.16/src/webview/webview_window.rs:313:30
  11: bowtie_ui::run::{{closure}}
             at ./src/lib.rs:127:13
  12: core::ops::function::FnOnce::call_once{{vtable.shim}}
             at /rustc/7cf61ebde7b22796c69757901dd346d0fe70bd97/library/core/src/ops/function.rs:250:5
  13: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
             at /rustc/7cf61ebde7b22796c69757901dd346d0fe70bd97/library/alloc/src/boxed.rs:2015:9
  14: tauri::app::setup
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-2.0.0-beta.16/src/app.rs:1798:5
  15: tauri::app::App<R>::run::{{closure}}
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-2.0.0-beta.16/src/app.rs:935:25
  16: tauri_runtime_wry::handle_event_loop
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-runtime-wry-2.0.0-beta.13/src/lib.rs:3208:7
  17: <tauri_runtime_wry::Wry<T> as tauri_runtime::Runtime<T>>::run::{{closure}}
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tauri-runtime-wry-2.0.0-beta.13/src/lib.rs:2521:7
  18: <tao::platform_impl::platform::app_state::EventLoopHandler<T> as tao::platform_impl::platform::app_state::EventHandler>::handle_nonuser_event::{{closure}}
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tao-0.27.0/src/platform_impl/macos/app_state.rs:105:9
  19: tao::platform_impl::platform::app_state::EventLoopHandler<T>::with_callback
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tao-0.27.0/src/platform_impl/macos/app_state.rs:79:7
  20: <tao::platform_impl::platform::app_state::EventLoopHandler<T> as tao::platform_impl::platform::app_state::EventHandler>::handle_nonuser_event
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tao-0.27.0/src/platform_impl/macos/app_state.rs:100:5
  21: tao::platform_impl::platform::app_state::Handler::handle_nonuser_event
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tao-0.27.0/src/platform_impl/macos/app_state.rs:208:11
  22: tao::platform_impl::platform::app_state::AppState::launched
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tao-0.27.0/src/platform_impl/macos/app_state.rs:299:5
  23: tao::platform_impl::platform::app_delegate::did_finish_launching
             at /Users/blarsen/.cargo/registry/src/index.crates.io-6f17d22bba15001f/tao-0.27.0/src/platform_impl/macos/app_delegate.rs:100:3

### Additional context

Replacing "about:blank" with "blank.html" fixes the problem.

The issue is webview.rs line 253, `window_url.host().unwrap()`.   I imagine replacing with `unwrap_or_default()` would fix the crash.