(closes issue #13891)

(closes issue #13891)
Reported by: smurfix

This reverts a change I made in 116297. At the time it seemed the change was required to solve an issue with attempting a transfer but then letting it timeout without dialing any digits. However, I didn't realize that having an empty extension was possible. I'm removing the immediate return that was added in pbx_find_extension if the extension is null.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@156649 65c4cc65-6c06-0410-ace0-fbb531ad65f3