users with no logins have no last_login
users with no logins have no last_login

fixes CANVAS-HYQ4

Change-Id: I4d7869f9954866edb2dd90994d2c3aae64d83a77
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/292136
QA-Review: Ben Rinaca <55a6093a45d41fed7a0fcf1e8dbdc41f5092bc04@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Isaac Moore <258108225390078ef47d1319acab49ad7948abf1@instructure.com>
Product-Review: Ben Rinaca <55a6093a45d41fed7a0fcf1e8dbdc41f5092bc04@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms