Prevent chanspy from binding to zombie channels

This patch addresses a bug with chanspy on local channels which roughly 50% of the time
would create a situation where chanspy can latch onto a zombie channel, keeping the zombie
alive forever and causing the channel doing the spying to never be able to hang up.

(closes issue ASTERISK-19493)
Reported by: lvl
Review: https://reviewboard.asterisk.org/r/1819/
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Merged revisions 359892 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 359898 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@359905 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_chanspy.c

@@ -529,7 +529,8 @@ static int channel_spy(struct ast_channel *chan, struct ast_autochan *spyee_auto
 
 	/* We now hold the channel lock on spyee */
 
-	if (ast_check_hangup(chan) || ast_check_hangup(spyee_autochan->chan)) {
+	if (ast_check_hangup(chan) || ast_check_hangup(spyee_autochan->chan) ||
+			ast_test_flag(ast_channel_flags(spyee_autochan->chan), AST_FLAG_ZOMBIE)) {
 		return 0;
 	}