FIX don't break if we only found a weak constraint in the cache.
FIX don't break if we only found a weak constraint in the cache.

massmutual/pystruct,d-mittal/pystruct,pystruct/pystruct,d-mittal/pystruct,amueller/pystruct,amueller/pystruct,massmutual/pystruct,pystruct/pystruct,wattlebird/pystruct,wattlebird/pystruct