add back code that got lost

src/webpack/webpack.ts

@@ -338,6 +338,9 @@ export function waitFor(filter: string | string[] | FilterFn, callback: Callback
     else if (typeof filter !== "function")
         throw new Error("filter must be a string, string[] or function, got " + typeof filter);
 
+    const [existing, id] = find(filter!, { isIndirect: true, isWaitFor: true });
+    if (existing) return void callback(existing, id);
+
     subscriptions.set(filter, callback);
 }