Ensure col is not None when retrieving quick populators

Ensure col is not None when retrieving quick populators

Fixed bug where an :func:`.undefer_group` option would not be recognized
if it extended from a relationship that was loading using joined eager
loading.

In particular we need to double check the column both in terms of
the given "adapter" as well as without applying the "adapter"
when searching for the column in the result.

As we now avoid redoing the row processor step we also
improve on callcounts in joined eager loading.

Change-Id: I0f48766f12f7299f4626ff41a00bf1f5bfca5f3b
Fixes: #4048