Add a background brush to the window

So the background always gets cleared out when the window resizes.

src/wine-host/editor.cpp

@@ -666,6 +666,7 @@ ATOM register_window_class(std::string window_class_name) {
     window_class.lpfnWndProc = window_proc;
     window_class.hInstance = GetModuleHandle(nullptr);
     window_class.hCursor = LoadCursor(nullptr, IDC_ARROW);
+    window_class.hbrBackground = CreateSolidBrush(RGB(32, 32, 32));
     window_class.lpszClassName = window_class_name.c_str();
 
     return RegisterClassEx(&window_class);