avcodec/alsdec: Fix integer overflow with shifting samples

Fixes: signed integer overflow: -346039050 * 8 cannot be represented in type 'int'
Fixes: 15283/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5692700268953600

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit a3bd4b260e)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/alsdec.c

@@ -1038,7 +1038,7 @@ static int decode_block(ALSDecContext *ctx, ALSBlockData *bd)
 
     if (*bd->shift_lsbs)
         for (smp = 0; smp < bd->block_length; smp++)
-            bd->raw_samples[smp] <<= *bd->shift_lsbs;
+            bd->raw_samples[smp] = (unsigned)bd->raw_samples[smp] << *bd->shift_lsbs;
 
     return 0;
 }