Better support for user accounts (#349)

* Better support for user accounts

* Nits

* Check for invalid ids

Ryujinx.HLE/OsHle/Services/Aud/IAudioDevice.cs

@@ -1,6 +1,7 @@
 using Ryujinx.HLE.Logging;
 using Ryujinx.HLE.OsHle.Handles;
 using Ryujinx.HLE.OsHle.Ipc;
+using Ryujinx.HLE.OsHle.SystemState;
 using System.Collections.Generic;
 using System.Text;