wmalosslessdec: Fix reading too many bits in decode_channel_residues()

Fixes a part of CVE-2012-2795

CC:libav-stable@libav.org

Based on a patch by Michael Niedermayer <michaelni@gmx.at>

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind

libavcodec/wmalosslessdec.c

@@ -520,7 +520,7 @@ static int decode_channel_residues(WmallDecodeCtx *s, int ch, int tile_size)
             residue = quo;
         else {
             rem_bits = av_ceil_log2(ave_mean);
-            rem      = rem_bits ? get_bits(&s->gb, rem_bits) : 0;
+            rem      = rem_bits ? get_bits_long(&s->gb, rem_bits) : 0;
             residue  = (quo << rem_bits) + rem;
         }