It causes other issues:
- It *will* break projects
- Stack traces from errors in extensions are unusable
- We do not even get some of the originally intended benefits like parallel loading
If the URL is already loaded, resolve immediately.
Fixes https://github.com/TurboWarp/scratch-gui/issues/637
Caused by TWStateManager repeatedly calling loadExtensionURL on locale
change.
This could be fixed in GUI, but fixing it in VM is easier and loading
multiple instances of the same extension doesn't make sense anyways.