fix model_name wrong variable

app.py

@@ -82,7 +82,7 @@ def infer(use_custom_model, model_name, custom_lora_weight, image_in, prompt, ne
     
     if use_custom_model:
         
-        if custom_model == "":
+        if model_name == "":
             raise gr.Error("you forgot to set a custom model name.")
         
         custom_model = model_name