Add null check for context in onRefresh.

* Added null check as a precaution to prevent the app from crashing.
* Removed call to checkUriAndScheduleCheckIfNeeded on receiving private
  profile available broadcast, to prevent call to onRefresh from getting
  added to the Handler.

Bug: 374276432
Test: Manual
Flag: EXEMPT bugfix
Change-Id: I12f6c838f044b2baaa501d527b93ba5ac7f891c0