gnrc_netreg: make message queue check more readable

sys/net/gnrc/netreg/gnrc_netreg.c

@@ -39,13 +39,14 @@ void gnrc_netreg_init(void)
 
 int gnrc_netreg_register(gnrc_nettype_t type, gnrc_netreg_entry_t *entry)
 {
-#ifdef DEVELHELP
-#if defined(MODULE_GNRC_NETAPI_MBOX) || defined(MODULE_GNRC_NETAPI_CALLBACKS)
+#if DEVELHELP
+
+# if defined(MODULE_GNRC_NETAPI_MBOX) || defined(MODULE_GNRC_NETAPI_CALLBACKS)
     bool has_msg_q = (entry->type != GNRC_NETREG_TYPE_DEFAULT) ||
-                     sched_threads[entry->target.pid]->msg_array;
-#else
-    bool has_msg_q = sched_threads[entry->target.pid]->msg_array;
-#endif
+                     (sched_threads[entry->target.pid]->msg_array != NULL);
+# else
+    bool has_msg_q = (sched_threads[entry->target.pid]->msg_array != NULL);
+# endif
 
     /* only threads with a message queue are allowed to register at gnrc */
     if (!has_msg_q) {
@@ -53,7 +54,7 @@ int gnrc_netreg_register(gnrc_nettype_t type, gnrc_netreg_entry_t *entry)
                   "using msg_init_queue() !!!!\n\n", entry->target.pid);
     }
     assert(has_msg_q);
-#endif
+#endif /* DEVELHELP */
 
     if (_INVALID_TYPE(type)) {
         return -EINVAL;