Turning subtitles off (or hiding them) while an ASS/SSA cue was on screen left
that cue painted until its natural end time on the ExoPlayer backend: AssHandler
nulls the libass track, after which every render returns null, no payload ever
reaches the GL thread again, and the overlay keeps its last swapped atlas. The
existing invalidateSubtitles() call from the #1387 fix could never repaint it.
The atlas pipeline now detects a trackless render request and hands the GL
thread one zero-quad payload, which clears and swaps a transparent frame. The
clear is keyed on the renderer state generation so one dropped as stale is
retried, and it self-heals from per-video-frame requests while playing; the
existing invalidate on the disable transition covers the paused case.
close#1884
edde746
eaccef33dc