avcodec/alsdec: Fix integer overflows of raw_samples in decode_var_block_data()

This also makes the code consistent with the existing similar MUL64()
in decode_var_block_data()

Fixes: signed integer overflow: -7277630735906765035 + -3272193951413647896 cannot be represented in type 'long'
Fixes: 16015/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5666552818434048

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 fad3ec89b7)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/alsdec.c

@@ -918,7 +918,7 @@ static int decode_var_block_data(ALSDecContext *ctx, ALSBlockData *bd)
             y = 1 << 6;
 
             for (base = begin; base < end; base++, tab++)
-                y += MUL64(bd->ltp_gain[tab], raw_samples[base]);
+                y += (uint64_t)MUL64(bd->ltp_gain[tab], raw_samples[base]);
 
             raw_samples[ltp_smp] += y >> 7;
         }
@@ -930,7 +930,7 @@ static int decode_var_block_data(ALSDecContext *ctx, ALSBlockData *bd)
             y = 1 << 19;
 
             for (sb = 0; sb < smp; sb++)
-                y += MUL64(lpc_cof[sb], raw_samples[-(sb + 1)]);
+                y += (uint64_t)MUL64(lpc_cof[sb], raw_samples[-(sb + 1)]);
 
             *raw_samples++ -= y >> 20;
             parcor_to_lpc(smp, quant_cof, lpc_cof);