Make sure our window has mouse focus before processing raw input events.

This happens rarely, but not reproducibly, where we get raw input events for the window even though it doesn't have focus.

src/video/windows/SDL_windowsevents.c

@@ -417,7 +417,7 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
             RAWINPUT inp;
             UINT size = sizeof(inp);
 
-            if (!mouse->relative_mode || mouse->relative_mode_warp) {
+            if (!mouse->relative_mode || mouse->relative_mode_warp || mouse->focus != data->window) {
                 break;
             }