Fix for Pub/Sub system, introduced in Redis 2.2.6 with the new copy-on-write...

Fix for Pub/Sub system, introduced in Redis 2.2.6 with the new copy-on-write safe iterator semantics. In the hope this is the last bug I introduced this way.

src/pubsub.c

@@ -141,7 +141,7 @@ int pubsubUnsubscribePattern(redisClient *c, robj *pattern, int notify) {
 /* Unsubscribe from all the channels. Return the number of channels the
  * client was subscribed from. */
 int pubsubUnsubscribeAllChannels(redisClient *c, int notify) {
-    dictIterator *di = dictGetIterator(c->pubsub_channels);
+    dictIterator *di = dictGetSafeIterator(c->pubsub_channels);
     dictEntry *de;
     int count = 0;