asyncwrap: fix nullptr parent check

The nullptr check for parent on entry to the constructor should be ==
not !=. This allows reqs that have a parent to run their own init hook
callbacks even if kCallInitHook has been disabled.

src/async-wrap-inl.h

@@ -23,7 +23,7 @@ inline AsyncWrap::AsyncWrap(Environment* env,
   // Check user controlled flag to see if the init callback should run.
   if (!env->using_asyncwrap())
     return;
-  if (!env->call_async_init_hook() && parent != nullptr)
+  if (!env->call_async_init_hook() && parent == nullptr)
     return;
 
   // TODO(trevnorris): Until it's verified all passed object's are not weak,