Don't initialize the first parameter of _BitScanForward* functions

Like the document example, no need to initialize `r` to 0.
https://docs.microsoft.com/en-us/cpp/intrinsics/bitscanforward-bitscanforward64

lib/compress/zstd_lazy.c

@@ -882,7 +882,7 @@ static U32 ZSTD_VecMask_next(ZSTD_VecMask val) {
     assert(val != 0);
 #   if defined(_MSC_VER) && defined(_WIN64)
     {
-        unsigned long r = 0;
+        unsigned long r;
         /* _BitScanForward64 is not defined outside of x64 */
         return _BitScanForward64(&r, val) ? (U32)r : 0;
     }