Do not bother with line colors if line_number_gutter is not yet calculated

[miv391]

Fixes #81135

When code files are changed with an external editor, all files in script list are reloaded. Files are validated and then _update_errors() is called for each file and type safe lines are colored by _update_errors() calling TextEdit's set_line_gutter_item_color() with line_number_gutter as a parameter. line_number_gutter is however calculated only when a file is opened to the edit view. When a project is opened, only one file is opened to edit view and only that file's line_number_gutter is calculated. If any file is now saved in external editor, all other files have line_number_gutter == -1 and the error message "Index p_gutter = -1 is out of bounds" is spawned for every line of those files. If the user opens all files in script list to the edit view before saving in the external editor, every file will have it's line_number_gutter calculated and there will be no errors.

This is now fixed simply by skipping the setting of line colors altogether if the line_number_gutter is not yet calculated. The script is not shown, so it doesn't matter. When the user opens the script file to the edit view, line_number_gutter is calculated and also _update_errors() is called again.

This is now fixed by not calling _validate_script() from reload_text() if editor_enabled == false.

[Paulb23]

Thanks for the detailed description!

Looks like the root cause is the editor lazy loading, as you pointed out. Once the tab is loaded _validate_script is connected / called. So we should probably not call it in the first place if the editor is not enabled, as there might be other things in an unexpected state. Would guess it's called from reload_text.

[akien-mga]

@miv391 Would you be able to look into @Paulb23's suggestion for fixing the issue earlier on?

I tried to reproduce #81135 myself to see if I could do it but didn't manage to trigger the problem in 4.3.dev so far.

[miv391]

I cannot reproduce the bug with v4.3.dev2.official either.

Edit: Yes, I can reproduce the bug after all.

[Calinou]

It might be worth adding a comment to describe why this early return is here.

[miv391]

The fix changed completely. The current fix is a bit more self explanatory.

[Calinou]

I can reproduce the original issue with the MRP from #81135 in 4.3.dev 7d2ca2d, and this PR fixes it (Linux + VS Code).

[miv391]

I tried the solution suggested by Paulb23 and it seems to work, so I changed what this fix does. Now _validate_script is not called at all if editor_enabled == false. So even less is done if the file is not yet opened in the edit view.

Requested changes done, presumably.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 4.2.2.