Fix window exiting with no message to user if _create_window fails

platform/windows/display_server_windows.cpp

@@ -6400,7 +6400,10 @@ DisplayServerWindows::DisplayServerWindows(const String &p_rendering_driver, Win
 	}
 
 	WindowID main_window = _create_window(p_mode, p_vsync_mode, p_flags, Rect2i(window_position, p_resolution), false, INVALID_WINDOW_ID);
-	ERR_FAIL_COND_MSG(main_window == INVALID_WINDOW_ID, "Failed to create main window.");
+	if (main_window == INVALID_WINDOW_ID) {
+		r_error = ERR_UNAVAILABLE;
+		ERR_FAIL_MSG("Failed to create main window.");
+	}
 
 	joypad = new JoypadWindows(&windows[MAIN_WINDOW_ID].hWnd);