avcodec/wavpack: Fix runtime error: left shift of negative value -2

Fixes: 723/clusterfuzz-testcase-6471394663596032

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit ba15005132)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/wavpack.c

@@ -736,13 +736,13 @@ static int wavpack_decode_block(AVCodecContext *avctx, int block_no,
             }
             for (i = 0; i < weights; i++) {
                 t = (int8_t)bytestream2_get_byte(&gb);
-                s->decorr[s->terms - i - 1].weightA = t << 3;
+                s->decorr[s->terms - i - 1].weightA = t * (1 << 3);
                 if (s->decorr[s->terms - i - 1].weightA > 0)
                     s->decorr[s->terms - i - 1].weightA +=
                         (s->decorr[s->terms - i - 1].weightA + 64) >> 7;
                 if (s->stereo_in) {
                     t = (int8_t)bytestream2_get_byte(&gb);
-                    s->decorr[s->terms - i - 1].weightB = t << 3;
+                    s->decorr[s->terms - i - 1].weightB = t * (1 << 3);
                     if (s->decorr[s->terms - i - 1].weightB > 0)
                         s->decorr[s->terms - i - 1].weightB +=
                             (s->decorr[s->terms - i - 1].weightB + 64) >> 7;