ari endpoints: GET /ari/endpoints/{invalid-tech} should return a 404

Was returning a 404 on a valid technology with an empty list of endpoints.
Now checking against the channel tech to make sure the tech itself is valid
and not just an empty list of endpoints.

(issue ASTERISK-22803)
Reported by: David M. Lee
........

Merged revisions 402793 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@402795 65c4cc65-6c06-0410-ace0-fbb531ad65f3