avoid truncation warning on MSVC

include/rapidjson/reader.h

@@ -224,7 +224,7 @@ inline const char *SkipWhitespace_SIMD(const char* p) {
 		x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w1));
 		x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w2));
 		x = _mm_or_si128(x, _mm_cmpeq_epi8(s, w3));
-		unsigned short r = ~_mm_movemask_epi8(x);
+		unsigned short r = (unsigned short)~_mm_movemask_epi8(x);
 		if (r == 0)	// all 16 characters are whitespace
 			p += 16;
 		else {		// some of characters may be non-whitespace