avcodec/snowdec: Fix runtime error: signed integer overflow: 1404 * 8388608...

avcodec/snowdec: Fix runtime error: signed integer overflow: 1404 * 8388608 cannot be represented in type 'int'

Fixes: 2004/clusterfuzz-testcase-minimized-5533262866808832

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

libavcodec/snowdec.c

@@ -228,9 +228,9 @@ static void dequantize_slice_buffered(SnowContext *s, slice_buffer * sb, SubBand
         for(x=0; x<w; x++){
             int i= line[x];
             if(i<0){
-                line[x]= -((-i*qmul + qadd)>>(QEXPSHIFT)); //FIXME try different bias
+                line[x]= -((-i*(unsigned)qmul + qadd)>>(QEXPSHIFT)); //FIXME try different bias
             }else if(i>0){
-                line[x]=  (( i*qmul + qadd)>>(QEXPSHIFT));
+                line[x]=  (( i*(unsigned)qmul + qadd)>>(QEXPSHIFT));
             }
         }
     }