Fix replication retry is still active when the replicator is offline
Fix replication retry is still active when the replicator is offline

* When the replicator is offline, also cancel the retryIfRetry delayed call.

* This also fixes #794 issue caused by a race condition when a pull replicator becomes online and the retryIfRetry is called about at the same time but before fetchRemoteCheckpoint is done. If this happens, two beginReplicating will be called and results to crash as the changeTracker will be started twice.

amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios