small fix for kojihub tonight

[Mike McLean]

There is a bug in kojihub that is blocking deletion of some builds. The
fix is very small and will only affect garbage collection. After talking
with mmcgrath, I'm planning on applying this fix to koji.fp.o tonight
and restarting the hub. I'll choose a time when the build queue is empty
(or at least sparse).

The patch is here:
https://hosted.fedoraproject.org/koji/changeset/eb1c53de6e3bea423864dd260f1f5bd3ae77ba6d