Fix: rm think if stream is Flase. (#5458)

### What problem does this PR solve?


### Type of change

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

api/db/services/dialog_service.py

@@ -194,7 +194,7 @@ def chat(dialog, messages, stream=True, **kwargs):
                 if isinstance(think, str):
                     thought = think
                     knowledges = [t for t in think.split("\n") if t]
-                else:
+                elif stream:
                     yield think
         else:
             kbinfos = retriever.retrieval(" ".join(questions), embd_mdl, tenant_ids, dialog.kb_ids, 1, dialog.top_n,