don't unlock a channel we didn't lock

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@6486 65c4cc65-6c06-0410-ace0-fbb531ad65f3

pbx.c

@@ -4881,6 +4881,7 @@ int ast_pbx_outgoing_exten(const char *type, int format, void *data, int timeout
 					ast_verbose(VERBOSE_PREFIX_4 "Channel %s was answered.\n", chan->name);
 
 				if (sync > 1) {
+					if (channel)
 						ast_mutex_unlock(&chan->lock);
 					if (ast_pbx_run(chan)) {
 						ast_log(LOG_ERROR, "Unable to run PBX on %s\n", chan->name);