fixes text support in sdp answer

The code that handled setting 'm=text' in the sdp was not executing
in the correct order.  The check to see if text was needed came after
the check to add 'm=text' to the sdp, this resulted in 'm=text' always
being set to 0 because it looked like text was never required.

(closes issue #16457)
Reported by: peterj
Patches:
      textportinsdp.diff uploaded by peterj (license 951)
      issue16457.diff uploaded by dvossel (license 671)
Tested by: peterj


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@239427 65c4cc65-6c06-0410-ace0-fbb531ad65f3