avoid double hash entry lookup
avoid double hash entry lookup

Summary:
Another minor thing I noticed in this code.

`.entry()` does the lookup and allows us to update an existing or insert into the empty entry.

Reviewed By: alunyov

Differential Revision: D21664521

fbshipit-source-id: 793c44654c59d0ca1cbb80297485c3117ccb684e

voideanvalue/relay,kassens/relay,kassens/relay,atxwebs/relay,wincent/relay,facebook/relay,xuorig/relay,wincent/relay,josephsavona/relay,voideanvalue/relay,xuorig/relay,yungsters/relay,atxwebs/relay,yungsters/relay,facebook/relay,josephsavona/relay,xuorig/relay,atxwebs/relay,voideanvalue/relay,facebook/relay,voideanvalue/relay,wincent/relay,kassens/relay,facebook/relay,atxwebs/relay,kassens/relay,yungsters/relay,facebook/relay,kassens/relay,voideanvalue/relay,wincent/relay,facebook/relay,xuorig/relay,xuorig/relay,kassens/relay,xuorig/relay,wincent/relay,wincent/relay,josephsavona/relay,voideanvalue/relay