Decoder: Increased allocation and added checks in sei parsing.

This prevents heap overflow while parsing sei_message.

Bug: 63122634
Test: ran PoC on unpatched/patched
Change-Id: I61c1ff4ac053a060be8c24da4671db985cac628c
(cherry picked from commit f2b70d353768af8d4ead7f32497be05f197925ef)
