Decoder: Fixes an out of bound write in bitstream buffer

[for mnc-dr-dev and later;  mnc-dev gets a different patch]

After emulation prevention, data is written as an int,
so at least 3 additional bytes should be available.
And since bitstream functions read 8 bytes ahead, 8 extra bytes
should be available in the bitstream buffer.

Bug: 33934721

Change-Id: I444ec6f85d01b0bade9f827e15c4b476779d6c69