XCLAIM: Create the consumer only on successful claims.

Fixes #6744.

src/t_stream.c

@@ -2246,7 +2246,7 @@ void xclaimCommand(client *c) {
     }
 
     /* Do the actual claiming. */
-    streamConsumer *consumer = streamLookupConsumer(group,c->argv[3]->ptr,1);
+    streamConsumer *consumer = NULL;
     void *arraylenptr = addReplyDeferredLen(c);
     size_t arraylen = 0;
     for (int j = 5; j <= last_id_arg; j++) {
@@ -2298,9 +2298,11 @@ void xclaimCommand(client *c) {
             if (nack->consumer)
                 raxRemove(nack->consumer->pel,buf,sizeof(buf),NULL);
             /* Update the consumer and idle time. */
+            if (consumer == NULL)
+                consumer = streamLookupConsumer(group,c->argv[3]->ptr,1);
             nack->consumer = consumer;
             nack->delivery_time = deliverytime;
-            /* Set the delivery attempts counter if given, otherwise 
+            /* Set the delivery attempts counter if given, otherwise
              * autoincrement unless JUSTID option provided */
             if (retrycount >= 0) {
                 nack->delivery_count = retrycount;