fix SQLCompiler.collection_name crash on QuerySet.update() with MTI#166

timgraham merged 2 commits intomongodb:mainmongodb/django-mongodb-backend:mainfrom

WaVEV:bugfix-QuerySet.update()-with-MTI-crashes-SQLCompiler.collection_name-with-StopIterationWaVEV/django-mongodb-backend:bugfix-QuerySet.update()-with-MTI-crashes-SQLCompiler.collection_name-with-StopIterationCopy head branch name to clipboard