Surface Flinger: Fix an oversight when closing a layer (#2192)

* Surface Flinger: Fix an oversight when closing a layer

As the title say.
I also took the liberty of changing the logic on how we select the
current layer being rendered to make it more explicit when opening and
creating layers.

NOTE: Found by Ac_k.

* check for RenderLayerId and not the dictionary size

This fix a possible race condition between the time you create a layer and set the one currently used for rendering

Ryujinx.HLE/HOS/Services/Vi/RootService/ApplicationDisplayService/IManagerDisplayService.cs

@@ -22,6 +22,7 @@ namespace Ryujinx.HLE.HOS.Services.Vi.RootService.ApplicationDisplayService
             long pid = context.Device.System.AppletState.AppletResourceUserIds.GetData<long>((int)appletResourceUserId);
 
             context.Device.System.SurfaceFlinger.CreateLayer(pid, out long layerId);
+            context.Device.System.SurfaceFlinger.SetRenderLayer(layerId);
 
             context.ResponseData.Write(layerId);