video_core: Allow changing background color while emulation is running

As @jroweboy stated, this is just one more atomic in VideoCore.

src/core/settings.cpp

@@ -31,6 +31,8 @@ void Apply() {
         VideoCore::g_emu_window->UpdateCurrentFramebufferLayout(layout.width, layout.height);
     }
 
+    VideoCore::g_renderer_bg_color_update_requested = true;
+
     if (Core::System::GetInstance().IsPoweredOn()) {
         Core::DSP().SetSink(values.sink_id, values.audio_device_id);
         Core::DSP().EnableStretching(values.enable_audio_stretching);