Fix clip interrogate from the webui

A recent change made the image RGBA, which makes the clip interrogator unhappy.
deepbooru and calling the interrogator from the api already do the conversion so this is the only place that needed it.

modules/ui.py

@@ -270,7 +270,7 @@ def apply_styles(prompt, prompt_neg, style1_name, style2_name):
 
 
 def interrogate(image):
-    prompt = shared.interrogator.interrogate(image)
+    prompt = shared.interrogator.interrogate(image.convert("RGB"))
 
     return gr_show(True) if prompt is None else prompt