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

This will avoid asserting incorrectly.
Backporting change from master branch into 2.5.0

Change-Id: Ibca0d69782f753e0dbb16652d5591a21e514c9f9
Reviewed-on: http://review.couchbase.org/29048
Reviewed-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>
Tested-by: Chiyoung Seo <8b279095f11c26cc21045fda5a3e51debb005aa9@gmail.com>
Reviewed-on: http://review.couchbase.org/29843
Reviewed-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>
Tested-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>

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