Fix shader graph assets loading to wait for async task

#3802

Source/Engine/Content/AssetsContainer.h

@@ -18,7 +18,7 @@ public:
     /// <param name="id">The asset id.</param>
     /// <returns>Loaded asset of null.</returns>
     template<typename T>
-    T* LoadAsync(const Guid& id)
+    T* Load(const Guid& id)
     {
         for (auto& e : *this)
         {
@@ -26,8 +26,10 @@ public:
                 return (T*)e.Get();
         }
         auto asset = (T*)::LoadAsset(id, T::TypeInitializer);
-        if (asset)
+        if (asset && !asset->WaitForLoaded())
             Add(asset);
+        else
+            asset = nullptr;
         return asset;
     }