Restore silent failure of a29981d

This restores the line added in a29981d
to make set_score() fail silently if the adjudicator is not on the
panel. It was removed by the merger of #1180, specifically in
a0eb1f7, which had been done long
before a29981d but not been merged until it was merged with #1180
(i.e., it was a merge conflict whose resolution appears to have
been overlooked).

Fixes #922.

tabbycat/results/result.py

@@ -927,7 +927,12 @@ def save(self):
                         defaults=self.get_defaults_fields('speakerscorebyadj', adj, side, pos))
 
     def set_score(self, adjudicator, side, position, score):
-        self.scoresheets[adjudicator].set_score(side, position, score)
+        try:
+            self.scoresheets[adjudicator].set_score(side, position, score)
+        except KeyError:
+            logger.exception("Tried to set score by adjudicator %s, but this adjudicator "
+                "doesn't have a scoresheet.", adjudicator)
+            return
 
     # --------------------------------------------------------------------------
     # Model fields