Fixed #16731 -- Made pattern lookups work properly with F() expressions

See https://code.djangoproject.com/ticket/16731#comment:11
Oh yes I see, it make sense, it returns the [`objs`](https://github.com/django/django/blob/e9103402c0fa873aea58a6a11dba510cd308cb84/django/db/models/query.py#L387-L423) passed, thanks.