* When settings are changed, we loop through the sync error map,
clearing mailboxes in the changed account that are in an error
state.
* It's possible that there are mailboxes referenced in the map that
no longer exist. When trying to retrieve them from the provider,
null is returned, but we're not checking for this case, and an
NPE results.
* The fix is simply to check for null, and clear the error map for
the mailboxId that references a deleted mailbox
Change-Id: I8c1c847090026fa1c53b09bbe6b12d864bce4df1
bdb28c1644