Move things around a bit more for onhold support, and add a check to only...

Move things around a bit more for onhold support, and add a check to only decrement the onhold variable if it's greater then 0. (issue #7740 reported by AuPix)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@40010 65c4cc65-6c06-0410-ace0-fbb531ad65f3