Never upscale images when thumbnailing

src/python/matrix_client.py

@@ -402,6 +402,7 @@ class MatrixClient(nio.AsyncClient):
             if small and is_jpg_png and not opaque_png:
                 raise UneededThumbnail()
 
+            if not small:
                 thumb.thumbnail((512, 512))
 
             with io.BytesIO() as out: