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>

libavcodec/wmalosslessdec.c

@@ -955,7 +955,8 @@ static int decode_subframe(WmallDecodeCtx *s)
                 else
                     use_normal_update_speed(s, i);
                 revert_cdlms(s, i, 0, subframe_len);
-            }
+            } else
+                memset(s->channel_residues, 0, sizeof(s->channel_residues));
     }
     if (s->do_mclms)
         revert_mclms(s, subframe_len);