Fix Image Comparer never populating its inherited IMAGE output.

The images output is never filled, and any link from it fails at runtime.

This also blocks the node inside ComfyUI's native Start Loop / End Loop, where
a node in the loop body must reach End Loop to pass validation and needs a
working output to connect to its terminations input.

Two optional inputs share one socket, so image_a is preferred and image_b is
the fallback.

py/image_comparer.py

@@ -39,4 +39,7 @@ class RgthreeImageComparer(PreviewImage):
     if image_b is not None and len(image_b) > 0:
       result['ui']['b_images'] = self.save_images(image_b, filename_prefix, prompt, extra_pnginfo)['ui']['images']
 
+    # RETURN_TYPES is inherited from SaveImage, so the node advertises an IMAGE
+    # output. Without a 'result' key it stays empty and any link from it fails.
+    result['result'] = (image_a if image_a is not None else image_b,)
     return result