Core dump if no widgets are visible

[white-haired-uncle]

Game and System Information

• Version:
  Battle for Wesnoth v1.19.0-dev (ebe84ce5e68-Modified)
• OS:
  Linux spartan 5.15.0-97-generic #107-Ubuntu SMP Wed Feb 7 13:26:48 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux

Description of the bug

Wanting to test that visible was a valid property of a stacked widget, I set it to visible=false and wesnoth crashed. I believe the cause is that it was the only widget and therefore there was nothing to display.

wesnoth: src/gui/widgets/widget.cpp:242: virtual void gui2::widget::place(const point&, const point&): Assertion `size.x >= 0' failed.
Abort(coredump)

Steps to reproduce the behavior

1. Start attached scenario
2. Use menu item 'stacked_widget_gui', wait 30 seconds or so for wesnoth to crash
3. Set visible on either widget, lines 1297 and/or 1298, repeat sequence with no crash

GUI_Tutorial.tar.gz

Expected behavior

A helpful error message

Additional context

This is a pretty stupid one that will probably never affect anyone else. But maybe it'll point to something that's worth fixing anyway.

[soliton-]

An assert that can be triggered by unexpected input is certainly worth fixing.