ENT-1334: Fix: SSO users last_login set to NULL
ENT-1334: Fix: SSO users last_login set to NULL

- The very first time a user signed in through SSO their ```last_login```
  field on the ```auth_user``` table was set to NULL instead of the
  appropriate time stamp.  This fixes that issue.

msegado/edx-platform,EDUlib/edx-platform,msegado/edx-platform,edx/edx-platform,stvstnfrd/edx-platform,stvstnfrd/edx-platform,jolyonb/edx-platform,angelapper/edx-platform,eduNEXT/edx-platform,mitocw/edx-platform,EDUlib/edx-platform,appsembler/edx-platform,ESOedX/edx-platform,ESOedX/edx-platform,arbrandes/edx-platform,msegado/edx-platform,arbrandes/edx-platform,cpennington/edx-platform,eduNEXT/edx-platform,edx/edx-platform,EDUlib/edx-platform,edx/edx-platform,ESOedX/edx-platform,angelapper/edx-platform,eduNEXT/edunext-platform,edx-solutions/edx-platform,arbrandes/edx-platform,jolyonb/edx-platform,mitocw/edx-platform,angelapper/edx-platform,jolyonb/edx-platform,eduNEXT/edunext-platform,EDUlib/edx-platform,eduNEXT/edx-platform,angelapper/edx-platform,eduNEXT/edunext-platform,msegado/edx-platform,appsembler/edx-platform,edx-solutions/edx-platform,eduNEXT/edx-platform,stvstnfrd/edx-platform,edx-solutions/edx-platform,mitocw/edx-platform,ESOedX/edx-platform,edx-solutions/edx-platform,edx/edx-platform,msegado/edx-platform,mitocw/edx-platform,cpennington/edx-platform,stvstnfrd/edx-platform,jolyonb/edx-platform,arbrandes/edx-platform,appsembler/edx-platform,cpennington/edx-platform,cpennington/edx-platform,eduNEXT/edunext-platform,appsembler/edx-platform