Properly close chat stream iterator even if response generation fails

Previously chat stream iterator wasn't closed when response streaming
for offline chat model threw an exception.

This would require restarting the application. Now application doesn't
hang even if current response generation fails with exception

src/khoj/processor/conversation/offline/chat_model.py

@@ -224,7 +224,7 @@ def llm_thread(g, messages: List[ChatMessage], model: Any, max_prompt_size: int
             g.send(response["choices"][0]["delta"].get("content", ""))
     finally:
         state.chat_lock.release()
-    g.close()
+        g.close()
 
 
 def send_message_to_model_offline(