Fix a race condition where the generator can go away

(closes issue #12175, reported by edantie, patched by me)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@107099 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/channel.c

@@ -1560,9 +1560,13 @@ static int generator_force(const void *data)
 	ast_channel_lock(chan);
 	tmp = chan->generatordata;
 	chan->generatordata = NULL;
-	generate = chan->generator->generate;
+	if (chan->generator)
+		generate = chan->generator->generate;
 	ast_channel_unlock(chan);
 
+	if (!tmp || !generate)
+		return 0;
+
 	res = generate(chan, tmp, 0, 160);
 
 	chan->generatordata = tmp;