avcodec/wmalosslessdec: Fixes undefined overflow in dequantization in decode_subframe()

Fixes: signed integer overflow: 47875596 * 45 cannot be represented in type 'int'
Fixes: 19082/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_WMALOSSLESS_fuzzer-5687766512041984

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/wmalosslessdec.c

@@ -979,7 +979,7 @@ static int decode_subframe(WmallDecodeCtx *s)
         if (s->quant_stepsize != 1)
             for (i = 0; i < s->num_channels; i++)
                 for (j = 0; j < subframe_len; j++)
-                    s->channel_residues[i][j] *= s->quant_stepsize;
+                    s->channel_residues[i][j] *= (unsigned)s->quant_stepsize;
     }
 
     /* Write to proper output buffer depending on bit-depth */