wmalosslessdec: Reset residues to 0 if they were not decoded from bitstream.

If channel residues are have not been decoded from bitstream, they should be
initialized to 0 instead of using values from previous subframe.
This causes bursts of noise in silent parts of some files.
This patch fixes bug #1055

Reviewed-by: Benjamin Larsson <benjamin@southpole.se>
Reviewed-by: Mashiat Sarker Shakkhar <mashiat.sarker@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
