Add timer ID attribute, for safe cleanup in the scripted environment

src/timer.c

@@ -8,7 +8,7 @@
 
 void mg_timer_init(struct mg_timer **head, struct mg_timer *t, uint64_t ms,
                    unsigned flags, void (*fn)(void *), void *arg) {
-  struct mg_timer tmp = {ms, 0U, 0U, flags, fn, arg, *head};
+  struct mg_timer tmp = {0U, ms, 0U, 0U, flags, fn, arg, *head};
   *t = tmp;
   *head = t;
 }