Fix the new send text manager command. There is no way this could have worked.

- Check the channel name string length to be zero, not non-zero
- Check the message string length to be zero, not non-zero
- unlock the channel *after* calling sendtext


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@46661 65c4cc65-6c06-0410-ace0-fbb531ad65f3