chat: join ChatLLM threads without calling destructors (#2043)

Signed-off-by: Jared Van Bortel <jared@nomic.ai>

gpt4all-chat/chatllm.cpp

@@ -95,6 +95,10 @@ ChatLLM::ChatLLM(Chat *parent, bool isServer)
 
 ChatLLM::~ChatLLM()
 {
+    destroy();
+}
+
+void ChatLLM::destroy() {
     m_stopGenerating = true;
     m_llmThread.quit();
     m_llmThread.wait();