alsdec: Check that quantized parcor coeffs are within range.

ALS spec:
	11.6.3.1.1 Quantization and encoding of parcor coefficients
	...
	In all cases the resulting quantized values ak are restricted to the range [-64,63].

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Justin Ruggles <justin.ruggles@gmail.com>
