Fix percent encoding to not encode digits.

lib/src/percent/encoder.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library convert.percent.encoder;
 
 import 'dart:convert';
 
 import 'package:charcode/ascii.dart';
 
@@ skipping 48 matching lines @@
   var byteOr = 0;
   for (var i = start; i < end; i++) {
     var byte = bytes[i];
     byteOr |= byte;
 
     // If the byte is an uppercase letter, convert it to lowercase to check if
     // it's unreserved. This works because uppercase letters in ASCII are
     // exactly `0b100000 = 0x20` less than lowercase letters, so if we ensure
     // that that bit is 1 we ensure that the letter is lowercase.
     var letter = 0x20 | byte;
+    // If the byte is a digit, convert it to its value. All other byte values
+    // are converted to a value greater than 9.
+    // Negative values are detected elsewhere.
+    var digit = 0x30 ^ byte;
     if ((letter >= $a && letter <= $z) ||
+        digit <= 9 ||
         byte == $dash ||
         byte == $dot ||
         byte == $underscore ||
         byte == $tilde) {
       // Unreserved characters are safe to write as-is.
       buffer.writeCharCode(byte);
       continue;
     }
 
     buffer.writeCharCode($percent);
@@ skipping 15 matching lines @@
         "Invalid byte ${byte < 0 ? "-" : ""}0x${byte.abs().toRadixString(16)}.",
         bytes, i);
   }
 
   throw 'unreachable';
 }
 
 /// Returns the ASCII/Unicode code unit corresponding to the hexadecimal digit
 /// [digit].
 int _codeUnitForDigit(int digit) => digit < 10 ? digit + $0 : digit + $A - 10;