improve UI when an error occurs during page load from checker
When the checker is loading a page or trying to find the question that someone submitted to, there are rare cases where an error can occur. Right now, the UI continues to report that "your submission is currently being checker" in that case, which is not true (since the error means we can't even start checking in that case).
Example: 6.009 staff trying to submit
'q000000' as a student, but the student doesn't actually have that box because
cs_post_load removes it from their view.
Process Process-173: Traceback (most recent call last): File "/usr/lib/python3.5/multiprocessing/process.py", line 249, in _bootstrap self.run() File "/usr/lib/python3.5/multiprocessing/process.py", line 93, in run self._target(*self._args, **self._kwargs) File "checker.py", line 148, in do_check question, args = namemap[name] KeyError: 'q000000'