avcodec/wavpack: Fix integer overflow

Fixes: runtime error: signed integer overflow: 227511904 + 1964113935 cannot be represented in type 'int'
Fixes: 2331/clusterfuzz-testcase-minimized-6182185830711296

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

libavcodec/wavpack.c

@@ -225,7 +225,7 @@ static int wv_get_value(WavpackFrameContext *ctx, GetBitContext *gb,
         INC_MED(1);
         DEC_MED(2);
     } else {
-        base = GET_MED(0) + GET_MED(1) + GET_MED(2) * (t - 2);
+        base = GET_MED(0) + GET_MED(1) + GET_MED(2) * (t - 2U);
         add  = GET_MED(2) - 1;
         INC_MED(0);
         INC_MED(1);