Fix following issues in blocking commands:

1. brpop last key index, thus checking all keys for slots.
2. Memory leak in clusterRedirectBlockedClientIfNeeded.
3. Remove while loop in clusterRedirectBlockedClientIfNeeded.

src/cluster.c

@@ -5438,6 +5438,7 @@ int clusterRedirectBlockedClientIfNeeded(client *c) {
                     clusterRedirectClient(c,node,slot,
                         CLUSTER_REDIR_MOVED);
                 }
+                dictReleaseIterator(di);
                 return 1;
             }
         }