Fix bad refactoring in quote.dart.

pkg/fasta/lib/src/quote.dart

 // Copyright (c) 2016, 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 fasta.quote;
 
 import 'errors.dart' show
     inputError,
     internalError;
 
@@ skipping 200 matching lines @@
           code = 0;
           for (int j = 0; j < 7; j++) {
             if (codeUnits.length == ++i) return error(i, incompleteSequence);
             int digit = codeUnits[i];
             if (j != 0 && digit == $CLOSE_CURLY_BRACKET) break;
             if (!isHexDigit(digit)) return error(i, invalidCharacter);
             code = (code << 4) + hexDigitValue(digit);
           }
         } else {
           // Expect exactly 4 hex digits.
-          if (codeUnits.length < i + 4) return error(i, incompleteSequence);
+          if (codeUnits.length <= i + 4) return error(i, incompleteSequence);
           code = 0;
           for (int j = 0; j < 4; j++) {
-            int digit = codeUnits[i];
+            int digit = codeUnits[++i];
             if (!isHexDigit(digit)) return error(i, invalidCharacter);
             code = (code << 4) + hexDigitValue(digit);
           }
         }
       } else {
         // Nothing, escaped character is passed through;
       }
       if (code > 0x10FFFF) return error(i, invalidCodePoint);
     }
     result[resultOffset++] = code;
   }
   return new String.fromCharCodes(result, 0, resultOffset);
 }