[interactive] #102 Move not-None assertions closer to usage

Because when running `bt test` for an interactive problem,
and `validator_error` and `team_error` are `False`,
the `.stderr` properties actually do not exist, and that's fine.

Author: mpsijm

bin/interactive.py

@@ -263,8 +263,6 @@ def get_validator_command():
         )
         submission_pid = submission.pid
 
-        assert validator.stderr and submission.stderr
-
         stop_kill_handler = threading.Event()
         submission_time: Optional[float] = None
 
@@ -387,9 +385,11 @@ def kill_handler_function():
 
         val_err = None
         if validator_error is False:
+            assert validator.stderr
             val_err = _feedback(run, validator.stderr.read())
         team_err = None
         if team_error is False:
+            assert submission.stderr
             team_err = submission.stderr.read().decode('utf-8', 'replace')
 
         if verdict == Verdict.TIME_LIMIT_EXCEEDED: