Ensure a11y ids for LabeledSeekBar are in bounds

Bug: 64124736
Test: I just played with it with TalkBack on. The crash
was difficult to reproduce before, and I can't make it
fail now. I believe I got it.

Change-Id: I17ffe8d83e21e716d1c0cadea52afcf09bff6e97
(cherry picked from commit 54ee713d)