MB-9147: lseek can return 0 if the file has no length
MB-9147: lseek can return 0 if the file has no length

This will avoid asserting incorrectly.

Change-Id: Ibca0d69782f753e0dbb16652d5591a21e514c9f9
Reviewed-on: http://review.couchbase.org/29048
Reviewed-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>
Tested-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>

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