Don't panic when getting refresh rate failed (#2533)

This fixes a crash on macOS when trying to get the monitor
refresh rate from the disabled monitor.

Co-authored-by: Jet Spark <lixiaopeng.jetspark@bytedance.com>
Co-authored-by: Mads Marquart <mads@marquart.dk>

src/platform_impl/windows/monitor.rs

@@ -192,7 +192,7 @@ impl MonitorHandle {
 
     #[inline]
     pub fn refresh_rate_millihertz(&self) -> Option<u32> {
-        let monitor_info = get_monitor_info(self.0).unwrap();
+        let monitor_info = get_monitor_info(self.0).ok()?;
         let device_name = monitor_info.szDevice.as_ptr();
         unsafe {
             let mut mode: DEVMODEW = mem::zeroed();