Error handling for unsupported transparency

When input images (palette mode) have transparency (bytes) in info,
the output images (RGB mode) will inherit it,
causing ValueError in Pillow:PIL/PngImagePlugin.py#1364
when trying to unpack this bytes.

This commit check the PNG mode and transparency info,
removing transparency if it's RGB mode and transparency is bytes

modules/images.py

@@ -548,6 +548,12 @@ def save_image_with_geninfo(image, geninfo, filename, extension=None, existing_p
         else:
             pnginfo_data = None
 
+        # Error handling for unsupported transparency in RGB mode
+        if (image.mode == "RGB" and
+            "transparency" in image.info and
+            isinstance(image.info["transparency"], bytes)):
+            del image.info["transparency"]
+
         image.save(filename, format=image_format, quality=opts.jpeg_quality, pnginfo=pnginfo_data)
 
     elif extension.lower() in (".jpg", ".jpeg", ".webp"):