Fixed test.py crashing on malformed test ids

Sometimes, if test_runner errors before running any tests, the last test
id can end up being None. This broke test output writing, which expected
to be able to parse an id. Instead we should just ignore the malformed
id (it's not like we can write anything relevant about any tests here),
and report it to the user at a higher level.

scripts/test.py

@@ -1085,7 +1085,7 @@ def run_stage(name, runner, test_ids, stdout_, trace_, output_, **args):
 
             except TestFailure as failure:
                 # keep track of failures
-                if output_:
+                if output_ and failure.id is not None:
                     case, _ = failure.id.split(':', 1)
                     suite = case_suites[case]
                     # get defines and write to csv