avcodec/flacdec: use get_unary() simplify code

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/ivi_common: make while get_bits loop more robust by checking bits left

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/ituh263dec: make while get_bits loop more robust by checking bits left

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/intelh263dec: make while get_bits loop more robust by checking bits left

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>