don't take the channel list lock until we're actually ready to put the new...

don't take the channel list lock until we're actually ready to put the new channel into the list in ast_channel_alloc (bug #3928)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@5352 65c4cc65-6c06-0410-ace0-fbb531ad65f3