Check for dirty events in specified account before syncing

* We were starting a sync if there was a dirty event in ANY of
  our Exchange accounts
* Change to check for the specific account before syncing; this
  saves provider queries and service (i.e. thread) startups

Bug: 2550620
Change-Id: I83e953f1bade9fa269b777e96121a63664e8edc8
1 file changed