fix: memory leak and crash when id is NULL in iq_id_handler_add (upstream 0218ba26)

src/xmpp/iq.c

@@ -358,6 +358,13 @@ _iq_id_handler_free(ProfIqHandler* handler)
 void
 iq_id_handler_add(const char* const id, ProfIqCallback func, ProfIqFreeCallback free_func, void* userdata)
 {
+    if (id == NULL) {
+        if (free_func) {
+            free_func(userdata);
+        }
+        return;
+    }
+
     ProfIqHandler* handler = malloc(sizeof(ProfIqHandler));
     if (handler) {
         handler->func = func;