Fix Out of Bounds Read in AAVCAssembler

Fixed Out of Bounds Read in dropFramesUntilIframe Function in
AAVCAssembler.
Added missing bound checks in pickStartSeq function of AHEVCAssembler.

Manual cherry-pick of pa/2300853.

Bug: 230630526

Change-Id: Ia9d0b172d0d09e3bf80a3b4bfc5d1125ac00264d
Test: Manual, See bug for repro steps.
(cherry picked from commit fa29e9f0)
Merged-In: Ia9d0b172d0d09e3bf80a3b4bfc5d1125ac00264d
(cherry picked from commit 3066b141)
Merged-In: Ia9d0b172d0d09e3bf80a3b4bfc5d1125ac00264d