Return to last channel watched from guide

Request: Pressing "back" from the guide will return to stream the last channel watched.

Current Behavior: Pressing "back" from the guide brings up the menu. Pressing "back" again exits to the Android TV menu. Both of these actions are redundant as you can get to the menu from the guide by pressing "left" and you can get to the Android TV menu by pressing home.

Current Workaround: pick any channel from the guide and then use the last-channel sequence to return to the last channel.

Configuration: Shield with Harmony Hub, exit button mapped to "back".