MB-6023 Move pending tasks to the dispatcher queue iff it's empty
MB-6023 Move pending tasks to the dispatcher queue iff it's empty

Change-Id: I46ce3c4b79ba9a4f1ba26e9b4662efadfe97ae8b
Reviewed-on: http://review.couchbase.org/18891
Reviewed-by: Liang Guo <863407acb9e207441ec9e80d0debd4fe4489aa9b@couchbase.com>
Tested-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>

abhinavdangeti/ep-engine,daverigby/kv_engine,owendCB/ep-engine,membase/ep-engine,couchbase/ep-engine,sriganes/ep-engine,abhinavdangeti/ep-engine,owendCB/ep-engine,membase/ep-engine,daverigby/ep-engine,sriganes/ep-engine,abhinavdangeti/ep-engine,jimwwalker/ep-engine,abhinavdangeti/ep-engine,teligent-ru/ep-engine,teligent-ru/ep-engine,daverigby/ep-engine,jimwwalker/ep-engine,jimwwalker/ep-engine,couchbase/ep-engine,owendCB/ep-engine,hisundar/ep-engine,teligent-ru/ep-engine,membase/ep-engine,daverigby/ep-engine,jimwwalker/ep-engine,couchbase/ep-engine,teligent-ru/ep-engine,hisundar/ep-engine,daverigby/ep-engine,hisundar/ep-engine,owendCB/ep-engine,sriganes/ep-engine,daverigby/kv_engine,hisundar/ep-engine,abhinavdangeti/ep-engine,daverigby/kv_engine,couchbase/ep-engine,sriganes/ep-engine,daverigby/kv_engine,membase/ep-engine