fix(wm): ensure window msg threads are stopped

This commit ensures that message handling threads for windows that are
created by komorebi are exited properly when the windows are destroyed.

For some reason, passing the HWND returned by CreateWindowExW to
GetMessageW continues returning TRUE even after the window has been
destroyed.

If HWND::NULL (via the Default trait) is passed to GetMessageW, which
retrieves messages for any window belonging to the current thread (our
threads here only own a single window), GetMessageW returns FALSE as
expected after the window is destroyed.

re #862

komorebi/src/border_manager/border.rs

@@ -98,13 +98,19 @@ impl Border {
             let hwnd = WindowsApi::create_border_window(PCWSTR(name.as_ptr()), h_module)?;
             hwnd_sender.send(hwnd)?;
 
-            let mut message = MSG::default();
-            unsafe {
-                while GetMessageW(&mut message, HWND(hwnd), 0, 0).into() {
-                    TranslateMessage(&message);
-                    DispatchMessageW(&message);
-                    std::thread::sleep(Duration::from_millis(10));
+            let mut msg: MSG = MSG::default();
+
+            loop {
+                unsafe {
+                    if !GetMessageW(&mut msg, HWND::default(), 0, 0).as_bool() {
+                        tracing::debug!("border window event processing thread shutdown");
+                        break;
+                    };
+                    TranslateMessage(&msg);
+                    DispatchMessageW(&msg);
                 }
+
+                std::thread::sleep(Duration::from_millis(10))
             }
 
             Ok(())