fix bug in web demo

src/utils/peft_trainer.py

@@ -49,6 +49,8 @@ class LogCallback(TrainerCallback):
         r"""
         Event called after logging the last logs.
         """
+        if "loss" not in state.log_history[-1]:
+            return
         cur_time = time.time()
         cur_steps = state.log_history[-1].get("step")
         elapsed_time = cur_time - self.start_time