Only send a SIGHUP if the pid is greater than -1, otherwise all PIDs greater...

Only send a SIGHUP if the pid is greater than -1, otherwise all PIDs greater than -1 will get the SIGHUP... and that is bad.
(closes issue #11453)
Reported by: alanmcmillan


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@92199 65c4cc65-6c06-0410-ace0-fbb531ad65f3