Fix syntax definition automatic assignment for syntax test files

[keith-hall]

This fixes the bug whereby opening a syntax_test_ file from OverrideAudit: Open Resource etc. would open without the syntax being assigned automatically from the syntax test header line.

The on_load event listener is fired before the file was read from the .sublime-package file, meaning the view is still empty, causing it to miss the syntax test header. So, this commit changes the behavior so that, if it sees that the file being loaded resides within the package catalog, and is empty, then it will re-try after a short delay.

[FichteFoll]

Hard timeouts like this are usually a thing we should try to avoid. Could we instead loop the function to itself and check for view.is_loading() instead of view.size() == 0? Unfortunately I wasn't able to reliably reproduce the issue (read: not even once) to check whether that also works myself.

Suggested change

	if view.size() == 0 and view.file_name().startswith(sublime.packages_path() + '/'):
	sublime.set_timeout(lambda: self.assign_syntax(view), 100)
	if view.is_loading() and view.file_name().startswith(sublime.packages_path() + '/'):
	sublime.set_timeout(lambda: self.on_load(view), 100)

[FichteFoll]

Was able to reproduce. Unfortuantely, view.is_loading is False despite the view still being empty, so my idea doesn't work here.
I honestly wish View.is_loading would be useful anywhere, but so far all I can remember is getting disappointed by it.