Call message_handlers_clear() upon disconnect

Free pubsub_event_handlers. Fix memory leaks.

src/xmpp/message.c

@@ -178,6 +178,14 @@ message_handlers_init(void)
     pubsub_event_handlers = g_hash_table_new_full(g_str_hash, g_str_equal, free, free);
 }
 
+void
+message_handlers_clear(void)
+{
+    if (pubsub_event_handlers) {
+        g_hash_table_remove_all(pubsub_event_handlers);
+    }
+}
+
 void
 message_pubsub_event_handler_add(const char *const node, ProfMessageCallback func, ProfMessageFreeCallback free_func, void *userdata)
 {