Fixed mis-use of set_image_model in automatic1111 Image generation

A custom model parameter would always throw an error.. :/

backend/open_webui/routers/images.py

@@ -623,7 +623,7 @@ async def image_generations(
             or request.app.state.config.IMAGE_GENERATION_ENGINE == ""
         ):
             if form_data.model:
-                set_image_model(form_data.model)
+                set_image_model(request, form_data.model)
 
             data = {
                 "prompt": form_data.prompt,