[WP8] When listening to music the screen should not automatically turn off

[tjsrowe]

Oh yes - additionally, and I'm going to log this as a bug because any basic music player should do this - but when connected to power, Spotify should not switch the screen off.

The last thing I want to have to do is unlock my phone and key in my pin just so I can go to the next track while I'm driving!  Other apps keep the screen active just fine; why was this missed in the WP8 version?