avcodec/wavpack: Check float_shift

Fixes: runtime error: shift exponent 40 is too large for 32-bit type 'unsigned int'
Fixes: 1898/clusterfuzz-testcase-minimized-5970744880136192

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 4020b009d1)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/wavpack.c

@@ -872,6 +872,12 @@ static int wavpack_decode_block(AVCodecContext *avctx, int block_no,
             s->float_flag    = bytestream2_get_byte(&gb);
             s->float_shift   = bytestream2_get_byte(&gb);
             s->float_max_exp = bytestream2_get_byte(&gb);
+            if (s->float_shift > 31) {
+                av_log(avctx, AV_LOG_ERROR,
+                       "Invalid FLOATINFO, shift = %d (> 31)\n", s->float_shift);
+                s->float_shift = 0;
+                continue;
+            }
             got_float        = 1;
             bytestream2_skip(&gb, 1);
             break;