User.get_profile() has checks in place to make use of any profile

fetched along with the user via select_related() or

prefetch_related().
In the case where the cached profile result is a None, we were falling

back on default behavior based on the create_if_missing flag. This is

fine if the flag is True (we want to create) but if the flag is

False a redundant fetch would occur, which would likely still return a

None result.
This code now respects a None entry in the cache in this case, which

will raise Profile.DoesNotExist as it would have before, but without

the redundant database query.
This will significantly speed up search indexing for users, which was

performing 4 queries per user.

Unit tests pass.
Built new unit tests (for an upcoming change) that found this issue and

verified the fix.