Fix incorrect memory tracking causing problems with memory_limit option.

Closes #1437. Thanks to Guillaume Bour.

ChangeLog.txt

@@ -1,6 +1,8 @@
 Broker:
 - Various fixes for `allow_zero_length_clientid` config, where this option was
   not being set correctly. Closes #1429.
+- Fix incorrect memory tracking causing problems with memory_limit option.
+  Closes #1437.
 
 Client library:
 - Fix publish properties not being passed to on_message_v5 callback for QoS 2

src/subs.c

@@ -684,7 +684,7 @@ struct mosquitto__subhier *sub__add_hier_entry(struct mosquitto__subhier *parent
 	}
 	child->parent = parent;
 	child->topic_len = len;
-	child->topic = malloc(len+1);
+	child->topic = mosquitto__malloc(len+1);
 	if(!child->topic){
 		child->topic_len = 0;
 		mosquitto__free(child);