Ensure chan->fdno always gets reset to -1 after handling a channel fd event.

Ensure chan->fdno always gets reset to -1 after handling a channel fd event.

Since setting fdno to -1 had to be moved, a couple of other code paths that
do process an fd event return early and do not pass through the code path
where it was moved to.  So, set it to -1 in a few other places, too.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@179741 65c4cc65-6c06-0410-ace0-fbb531ad65f3