fix(ai): unlock mutex before early return in error callback

The mutex was not released when the aiwin pointer was invalid, leading to a potential deadlock in the AI thread.

src/ai/ai_client.c

@@ -110,6 +110,7 @@ _aiwin_display_error(gpointer user_data, const gchar* error_msg)
     ProfAiWin* aiwin = _aiwin_validate(user_data);
     if (!aiwin) {
         log_warning("[AI-THREAD] Cannot display error: aiwin is invalid or window was closed (msg: %s)", error_msg);
+        pthread_mutex_unlock(&lock);
         return;
     }
     aiwin_display_error(aiwin, error_msg);