Fix parsing numbers which are less than 1e-308

Overflow should check sign of exponent.

include/rapidjson/reader.h

@@ -796,7 +796,7 @@ private:
 				exp = s.Take() - '0';
 				while (s.Peek() >= '0' && s.Peek() <= '9') {
 					exp = exp * 10 + (s.Take() - '0');
-					if (exp > 308)
+					if (exp > 308 && !expMinus) // exp > 308 should be rare, so it should be checked first.
 						RAPIDJSON_PARSE_ERROR(kParseErrorNumberTooBig, s.Tell());
 				}
 			}

test/unittest/readertest.cpp

@@ -137,6 +137,7 @@ TEST(Reader, ParseNumberHandler) {
 	TEST_DOUBLE("2.22507e-308", 2.22507e-308);
 	TEST_DOUBLE("-1.79769e+308", -1.79769e+308);
 	TEST_DOUBLE("-2.22507e-308", -2.22507e-308);
+	TEST_DOUBLE("4.9406564584124654e-324", 4.9406564584124654e-324); // minimum denormal
 	TEST_DOUBLE("18446744073709551616", 18446744073709551616.0);	// 2^64 (max of uint64_t + 1, force to use double)
 	TEST_DOUBLE("-9223372036854775809", -9223372036854775809.0);	// -2^63 - 1(min of int64_t + 1, force to use double)