fix bug of chat without stream (#830)

### What problem does this PR solve?

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/apps/conversation_app.py

@@ -162,10 +162,13 @@ def completion():
             return resp
 
         else:
-            ans = chat(dia, msg, **req)
-            fillin_conv(ans)
-            ConversationService.update_by_id(conv.id, conv.to_dict())
-            return get_json_result(data=ans)
+            answer = None
+            for ans in chat(dia, msg, **req):
+                answer = ans
+                fillin_conv(ans)
+                ConversationService.update_by_id(conv.id, conv.to_dict())
+                break
+            return get_json_result(data=answer)
     except Exception as e:
         return server_error_response(e)