This fixes a problem with services that doesn't implement GetAll() for
one reason or another.

$ gdbus introspect --session --dest org.freedesktop.ReserveDevice1.Audio0 --object-path /org/freedesktop/ReserveDevice1/Audio0
node /org/freedesktop/ReserveDevice1/Audio0 {
  interface org.freedesktop.ReserveDevice1 {
    methods:
      RequestRelease(in  i priority,
                     out b result);
    properties:
      readonly i Priority = 0;
      readonly s ApplicationName = 'PulseAudio Sound Server';
      readonly s ApplicationDeviceName = 'Internal Audio Analog Stereo';
  };
  interface org.freedesktop.DBus.Properties {
    methods:
      Get(in  s interface,
          in  s property,
          out v value);
  };
  interface org.freedesktop.DBus.Introspectable {
    methods:
      Introspect(out s data);
  };
};