fix: 修复undo按钮的bug

gradio_app.py

@@ -97,6 +97,8 @@ def get_gradio_demo(model, tokenizer, image_processor) -> gr.Interface:
             history: list[tuple[str, str]]) -> tuple[list[tuple[str, str]], str]:
         try:
             message, _ = history.pop()
+            if not isinstance(message, str):
+                message, _ = history.pop()
         except IndexError:
             message = ''
         return history, message or ''