File group directory picker should validate directories exists

[ascobie]

1. Go to create a file group page
2. Enter valid fg name and select a valid folder
3. Accidentally change the folder path and click create

Expected: Should see an error
Actual: I get a green success notification saying 0 files were uploaded, in the console there is the following error. No file group is created.

This may have been fixed by recent python error handling changes so will check when i get the latest version.

[ascobie]

No longer errors. But the submission just closes the form and no file group is created if the only added path was not valid. probably need to check in _uploadFileGroupData that we have > 0 valid paths and if not we show a warning to the user and block submission.