Fix the boxart not being found for some games.

I overthought this problem way too hard lmao

src/importer/sources/retroarch_source.py

@@ -81,7 +81,8 @@ class RetroarchSourceIterator(SourceIterator):
                 additional_data = {}
 
                 # Get boxart
-                boxart_image_name = item["label"].split(".", 1)[0] + ".png"
+                boxart_image_name = item["label"] + ".png"
+                boxart_image_name = boxart_image_name.replace("&", "_")
                 boxart_folder_name = playlist_file.name.split(".", 1)[0]
                 image_path = (
                     self.source.config_location["thumbnails"]