Fixed #10414 -- Make select_related fail on invalid field names.

https://code.djangoproject.com/ticket/10414

This is basically my first non-trivial contribution to Django, so it might not be perfect. I'll be happy to update the PR as required. :)
Basically a PEP8 E128 fix. This rule is for certain not turned on in the CI checks, but the internal docs does not seem to mention it as an exception from PEP8 either, so I would say that it is better to fix these errors when editing surrounding code. But yeah, it is definitely not a necessary change.