Fix: status checking in TimedTextDriver.

o fixes seeking error when there's no enabled text track.
o clean up status checking code for deselectTrack.
o fixes a potential bug : pause->backward seek can trigger unwanted
resume.

Bug: 6682160
Change-Id: I03d8788b27fb9c0a6092be83ad3578ccf3266905
(cherry picked from commit 2dafb6071d4f14e0e208912500694912211aa26b)