Fix ResourceItemLabelTest file-delete failure on Windows

[Copilot]

On Windows, files cannot be deleted while open. testBug566858_leadingWhitespace calls getStyleRanges three times with the same filename (" test.txt"), and the original code attempted to delete the file immediately after dialog.close() — before the OS had released the file handle, causing a ResourceException.

Change

• Removed file.delete(true, null) from after dialog.close()
• Added a guarded delete at the start of getStyleRanges: if the file already exists (left over from a previous call), delete it there — by which point the prior dialog is fully torn down and the lock released
• Final cleanup is handled by doTearDown, which deletes the whole project

// Before: delete immediately after close — fails on Windows if handle not yet released
dialog.close();
file.delete(true, null);  // ← boom on Windows

// After: delete at the start of the next call, when the prior dialog is gone
if (file.exists()) {
    file.delete(true, null);  // safe — previous dialog is fully closed
}
file.create(stream, true, new NullProgressMonitor());

[basilevs]

If the dialog leaks resources, should not it be fixed instead of relying on GC to close files? Why should test code adapted to a broken dialog?

[fedejeanne]

@basilevs I don't see anything in FilteredResourcesSelectionDialog that could indicate any leaking files. Can you please elaborate on that?

[basilevs]

@basilevs I don't see anything in FilteredResourcesSelectionDialog that could indicate any leaking files. Can you please elaborate on that?

That was a comment to a previous revision, where deletion of a file was postponed to accommodate a broken dialog.