swscale/swscale: Use unsigned operation to avoid undefined behavior

I have not checked that the constant is correct, this just fixes the undefined behavior

Fixes: signed integer overflow: -646656 * 3517 cannot be represented in type 'int
Fixes: 70559/clusterfuzz-testcase-minimized-ffmpeg_SWS_fuzzer-5209368631508992

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

libswscale/swscale.c

@@ -224,7 +224,7 @@ static void lumRangeFromJpeg16_c(int16_t *_dst, int width)
     int i;
     int32_t *dst = (int32_t *) _dst;
     for (i = 0; i < width; i++)
-        dst[i] = (dst[i]*(14071/4) + (33561947<<4)/4)>>12;
+        dst[i] = ((int)(dst[i]*(14071U/4) + (33561947<<4)/4)) >> 12;
 }