avoid shift out-of-range error

UBSAN gave during Reader.ParseNumber_FullPrecisionDouble test:
include/rapidjson/internal/strtod.h:149:11: runtime error: shift exponent 46 is too large for 32-bit type 'int'

include/rapidjson/internal/strtod.h

@@ -142,7 +142,7 @@ inline bool StrtodDiyFp(const char* decimals, size_t length, size_t decimalPosit
     size_t remaining = length - i;
     const unsigned kUlpShift = 3;
     const unsigned kUlp = 1 << kUlpShift;
-    int error = (remaining == 0) ? 0 : kUlp / 2;
+    int64_t error = (remaining == 0) ? 0 : kUlp / 2;
 
     DiyFp v(significand, 0);
     v = v.Normalize();