Fix some gcc warnings in `rugged_repo_new_with_backend`.
Fix some gcc warnings in `rugged_repo_new_with_backend`.

libgit2/rugged,libgit2/rugged,tpickett66/rugged,tpickett66/rugged,tpickett66/rugged,Acidburn0zzz/rugged,Acidburn0zzz/rugged,saraid/rugged,libgit2/rugged,Acidburn0zzz/rugged,saraid/rugged,saraid/rugged