Quit AccountObserver if EmailProvider is unavailable

* We were just returning an empty array in collectEasAccounts if
  the resulting cursor was null; this could cause callers to
  think an account had been deleted.
* Now, we throw ProviderUnavailableException in collectEasAccounts
  and simply return from the observer in this case

Bug: 5367821
Change-Id: I876a4f21093ea4d061804a6fcbb2d5a255e8cb8e
1 file changed