解决当request_output_len+input_id长度大于session_len时就不输出的问题，将策略改成自适应request_output_len，可以生成到session_len为止

lmdeploy/serve/async_engine.py

@@ -264,12 +264,18 @@ class AsyncEngine:
             prompt = self.model.messages2prompt(prompt, sequence_start)
         input_ids = self.tokenizer.encode(prompt, add_bos=sequence_start)
         finish_reason = None
+
+        request_output_len = min(
+                request_output_len, self.tm_model.session_len - self.id2step[str(session_id)] -
+                len(input_ids))
+        request_output_len = max(0, request_output_len)
+
         if stop is True:
             self.stop_session(session_id)
             yield GenOut('', self.id2step[str(session_id)], len(input_ids), 0,
                          finish_reason)
         elif self.id2step[str(session_id)] + len(
-                input_ids) + request_output_len >= self.tm_model.session_len:
+                input_ids) + request_output_len > self.tm_model.session_len:
             finish_reason = 'length'
             yield GenOut('', self.id2step[str(session_id)], len(input_ids), 0,
                          finish_reason)