timer: call list.start regardless new or not

Call start regardless whether list is new
or not to prevent incorrect active_handles
count.

Fixes nodejs#25831.

lib/timers.js

@@ -59,14 +59,17 @@ function insert(item, msecs) {
     list = lists[msecs];
   } else {
     list = new Timer();
-    list.start(msecs, 0);
 
     L.init(list);
 
     lists[msecs] = list;
     list.msecs = msecs;
     list[kOnTimeout] = listOnTimeout;
   }
+  // Call start regardless whether list is new
+  // or not to prevent incorrect active_handles
+  // count. See issue #25831.
+  list.start(msecs, 0);
 
   L.append(list, item);
   assert(!L.isEmpty(list)); // list is not empty