fix for syncing tile load events when cache primed

add a short timeout to check if any tiles have been queued and
cancel the listener if not. otherwise the deferred is never
done and playback hangs

remove check on deferred array as not needed, calling when
w/ empty array returns immediately

refs #6
Merge pull request #12 from MapStory/iss-6

fix for syncing tile load events when cache primed