[erts] Fix harmless initialization bug

Author: rickard-green

erts/emulator/beam/erl_proc_sig_queue.c

@@ -9021,11 +9021,9 @@ erts_proc_sig_queue_try_enqueue_to_buffer(Eterm from,
         int nonmsg = ERTS_SIG_IS_NON_MSG(first);
         int restarted = 0;
         ErtsSignalInQueueBuffer* buffer;
-        Uint64 nonempty_slots_before;
+        Uint64 nonempty_slots_before = 0;
         Uint32 slot, state;
 
-        ERTS_UNDEF(nonempty_slots_before, 0);
-
         ASSERT(is_value(from));
 
         /* Use the sender id to hash to an outer signal queue buffer. This