wmalosslessdec: make MCLMS arrays big enough for what is written into them.

Fixes a part of CVE-2012-2795

CC:libav-stable@libav.org

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Anton Khirnov <anton@khirnov.net>

libavcodec/wmalosslessdec.c

@@ -129,8 +129,8 @@ typedef struct WmallDecodeCtx {
     int8_t  mclms_scaling;
     int16_t mclms_coeffs[128];
     int16_t mclms_coeffs_cur[4];
-    int16_t mclms_prevvalues[64];
-    int16_t mclms_updates[64];
+    int16_t mclms_prevvalues[WMALL_MAX_CHANNELS * 2 * 32];
+    int16_t mclms_updates[WMALL_MAX_CHANNELS * 2 * 32];
     int     mclms_recent;
 
     int     movave_scaling;