Fix image upload without thumbnail

src/backend/matrix_client.py

@@ -631,6 +631,9 @@ class MatrixClient(nio.AsyncClient):
         path             = Path(await path() if callable(path) else path)
         encrypt          = room_id in self.encrypted_rooms
 
+        thumb_crypt_dict: Dict[str, Any] = {}
+        crypt_dict:       Dict[str, Any] = {}
+
         try:
             size = path.resolve().stat().st_size
         except (PermissionError, FileNotFoundError):