preemptive code in workflow gen for SD3

Author: mcmonkey4eva

src/BuiltinExtensions/ComfyUIBackend/WorkflowGenerator.cs

@@ -1268,6 +1268,13 @@ public bool IsCascade()
         return clazz is not null && clazz == "stable-cascade-v1";
     }
 
+    /// <summary>Returns true if the current model is Stable Diffusion 3.</summary>
+    public bool IsSD3()
+    {
+        string clazz = CurrentCompatClass();
+        return clazz is not null && clazz == "stable-diffusion-v3-medium";
+    }
+
     /// <summary>Gets a dynamic ID within a semi-stable registration set.</summary>
     public string GetStableDynamicID(int index, int offset)
     {
@@ -1806,6 +1813,15 @@ public string CreateEmptyImage(int width, int height, int batchSize, string id =
                 ["width"] = width
             }, id);
         }
+        else if (IsSD3())
+        {
+            return CreateNode("EmptySD3LatentImage", new JObject()
+            {
+                ["batch_size"] = batchSize,
+                ["height"] = height,
+                ["width"] = width
+            }, id);
+        }
         else if (UserInput.Get(ComfyUIBackendExtension.ShiftedLatentAverageInit, false))
         {
             double offA = 0, offB = 0, offC = 0, offD = 0;