Fix humanoid empty action queue

When the tickDay function sends a patient to the toilets, there
is a small timeframe (the time required for standing up), where the
tryToFindNearbyPatients function tries to reroute a patient who is
going to the toilet. The finishAction function is then called too
often and all actions from the action queue are consumed, so the error
message pops up.
Merge pull request #416 from phillipp/empty-action-queue-fix

Fix humanoid empty action queue