frontend: fix crash from running `status` on non-checked-out branch (MR 27)

`mrhlpr status 123` on a non-checked-out branch would panic because
`commits_follow_format` was an undefined variable.

mrhlpr/frontend.py

@@ -35,6 +35,8 @@ def print_status(mr_id, no_cache=False):
     clean_worktree = None
     commits = []
     commits_have_id = None
+    commits_follow_format = None
+    subj_err = []
     commits_are_signed = None
     target_branch = status["target_branch"]