Fix error message if user does not exist during startup
Fix error message if user does not exist during startup

(cherry picked from commit 945fb4479570d93196d1fd4b1b779a2126378ec6)

uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend,uroni/urbackup_backend