User commiting files through the web shouldn't allow empty commit messages

Summary

On our Gitaly sentry I've spotted the following:

*status.statusError: rpc error: code = InvalidArgument desc = UserCommitFiles: empty CommitMessage

Steps to reproduce

On your dev environment it should be possible to submit a new patch to create a commit. Its unclear to me if this is through the new WebIDE or the 'old' interface.

What is the current bug behavior?

User tries to create a commit without a message, and instead of disabling the submit button we try to actually do this. How the user gets feedback is unclear to me at the moment.

What is the expected correct behavior?

Not to post the commit to Gitaly, and provide feedback to the user earlier.

Results of GitLab environment info

GitLab.com running 10.5.X

Possible fixes

Both on the frontside, but also on the controller catch this.

/cc @timzallmann