Avoid some looping, add comment for clarity.

There's no need to check all the arenas -- as soon as one has knockout
matches we can assume they all do. The change here doesn't really
affect that logic as we're still only checking one match. We now
only check the first match we find, not the last.

Change-Id: I7e9f845e6997735116ccb63d82afe76f8980ff7d
Bump srcomp to pick up match_after fix.

Change-Id: If16346740fb4ba97251735564a5cd671e342ba6a