Merge branch 'fix/commit-no-repo-error' into 'master'

Fix broken repo error raised after requesting a commit

Prevents a 500 error on screen after `Rugged::RepositoryError: Could not find repository from '/var/opt/gitlab/git-data/repositories/user/project.git'`, which could happen when checking for the last commit in the list of projects (dashboard).

Related https://gitlab.com/gitlab-org/gitlab-ce/issues/20501

See merge request !124