v2.2/feature:disable clear if playlist empty

tower: https://tower.im/projects/d4e0ff64158645f28d99a9ca72d0c27b/todos/8d514fde371841e7acabaf6287e222f4/
tower: https://tower.im/projects/d4e0ff64158645f28d99a9ca72d0c27b/todos/f9dbab8c4b224d67b695b2406f669b28/

1, disable clear action if playlist if empty
2, fix the bug that subtitles menu selects the wrong one

Change-Id: I1484774b8e1bd253cc06a839370da968f7deee82