fix sticker resize

bots/modules/stickers.py

@@ -29,8 +29,15 @@ class StickersBotModuleConfig(TelegramBotModuleConfig):
                 f.seek(0)
                 im = Image.open(f).convert('RGBA')
         width, height = im.size
-        im.thumbnail((512, 512), Image.ANTIALIAS)
-        target_width, target_height = im.size
+        long_dimension = max(width, height)
+        scale_ratio = 512 / long_dimension
+        target_width = int(width * scale_ratio)
+        target_height = int(height * scale_ratio)
+        if long_dimension == width:
+            target_width = 512
+        else:
+            target_height = 512
+        im.resize((target_width, target_height), Image.ANTIALIAS)
         with tempfile.NamedTemporaryFile(suffix='.png') as f:
             im.save(f, 'png')
             f.seek(0)