Fixed 500 error when creating issue for project with no commits.

The form was updated to check that the repository wasn't empty before trying
to load the contribution guide.

This fixes #153.
 Merge branch 'bugfix/153/500_when_create_issue' into 'master'

Fix 500 Error When Creating Issue For Project With No Commits

This merge request fixes issue #153, where trying to create an issue for a project with no commits results in a 500 error. This was done by updating the form to check that the repository wasn't empty before trying to load the contribution guide.