GenericReader::ParseNumber: consistently use s.Tell()

The error messages in ParseNumber used `is.Tell` to report the
position of the number parsing error.  Depending on the copy
optimization of the current stream, this can lead to different
behaviour (beginning of number vs. position of error).

include/rapidjson/reader.h

@@ -610,7 +610,7 @@ private:
 				}
 		}
 		else
-			RAPIDJSON_PARSE_ERROR(kParseErrorValueInvalid, is.Tell());
+			RAPIDJSON_PARSE_ERROR(kParseErrorValueInvalid, s.Tell());
 
 		// Parse 64bit int
 		uint64_t i64 = 0;
@@ -643,7 +643,7 @@ private:
 			d = (double)i64;
 			while (s.Peek() >= '0' && s.Peek() <= '9') {
 				if (d >= 1E307)
-					RAPIDJSON_PARSE_ERROR(kParseErrorNumberTooBig, is.Tell());
+					RAPIDJSON_PARSE_ERROR(kParseErrorNumberTooBig, s.Tell());
 				d = d * 10 + (s.Take() - '0');
 			}
 		}
@@ -662,7 +662,7 @@ private:
 				--expFrac;
 			}
 			else
-				RAPIDJSON_PARSE_ERROR(kParseErrorNumberMissFraction, is.Tell());
+				RAPIDJSON_PARSE_ERROR(kParseErrorNumberMissFraction, s.Tell());
 
 			while (s.Peek() >= '0' && s.Peek() <= '9') {
 				if (expFrac > -16) {
@@ -695,11 +695,11 @@ private:
 				while (s.Peek() >= '0' && s.Peek() <= '9') {
 					exp = exp * 10 + (s.Take() - '0');
 					if (exp > 308)
-						RAPIDJSON_PARSE_ERROR(kParseErrorNumberTooBig, is.Tell());
+						RAPIDJSON_PARSE_ERROR(kParseErrorNumberTooBig, s.Tell());
 				}
 			}
 			else
-				RAPIDJSON_PARSE_ERROR(kParseErrorNumberMissExponent, is.Tell());
+				RAPIDJSON_PARSE_ERROR(kParseErrorNumberMissExponent, s.Tell());
 
 			if (expMinus)
 				exp = -exp;