Hi. I suggest to add a consule error message for the case when mw.loader.using gets an unexisting library parameter.

1. Open some user script with mw.loader.using.
2. Break one parameter. For example, change ooui to ooui5.
3. Save the script.
4. Check if it runs.
5. Expected: the script does not run, the console has a new error message "name not found".
6. Got: the script does not run, the console is empty.

It will definitely help to debugging process, knowing what's wrong. Thank you.