# Description
Fixes: nushell#12795

The issue is caused by an empty position of `ParseError::UnexpectedEof`.
So no detailed message is displayed.
To fix the issue, I adjust the start of span to `span.end - 1`. In this
way, we can make sure that it never points to an empty position.

After lexing item, I also reorder the unclosed character checking . Now
it will be checking unclosed opening delimiters first.

# User-Facing Changes
After this pr, it outputs detailed error message for incomplete string
when running scripts.

## Before
```
❯ nu -c "'ab"
Error: nu::parser::unexpected_eof

  × Unexpected end of code.
   ╭─[source:1:4]
 1 │ 'ab
   ╰────
> ./target/debug/nu -c "r#'ab"
Error: nu::parser::unexpected_eof

  × Unexpected end of code.
   ╭─[source:1:6]
 1 │ r#'ab
   ╰────
```
## After
```
> nu -c "'ab"
Error: nu::parser::unexpected_eof

  × Unexpected end of code.
   ╭─[source:1:3]
 1 │ 'ab
   ·   ┬
   ·   ╰── expected closing '
   ╰────
> ./target/debug/nu -c "r#'ab"
Error: nu::parser::unexpected_eof

  × Unexpected end of code.
   ╭─[source:1:5]
 1 │ r#'ab
   ·     ┬
   ·     ╰── expected closing '#
   ╰────
```


# Tests + Formatting
Added some tests for incomplete string.

---------

Co-authored-by: Ian Manske <ian.manske@pm.me>