Unmute Spotify on startup

[OpenByteDev]

When Spotify is muted when EZBlocker starts it does not unmute until the first transition from ad to normal song. This happens because it is assumed in the code that Spotify is unmuted when the application is started, even though this is never checked.

I changed the muted flag in Main from bool to bool? and the default value from false to null. A null value means that the state cannot be determined (probably because Spotify is closed).