Require a digit when parsing JSON number.

lib/json/json.dart

 // Copyright (c) 2011, 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("json");
 
 // Pure Dart implementation of JSON protocol.
 
 /**
  * Utility class to parse JSON and serialize objects to JSON.
@@ skipping 264 matching lines @@
   num _parseNumber() {
     if (!_isToken(NUMBER_LITERAL)) _error("Expected number literal");
 
     final int startPos = position;
     if (_isChar(MINUS)) position++;
     if (_isChar(CHAR_0)) {
       position++;
     } else if (_isDigit()) {
       position++;
       while (_isDigit()) position++;
+    } else {
+      _error("Expected digit when parsing number");
     }
 
     bool isInt = true;
     if (_isChar(DOT)) {
       position++;
       if (_isDigit()) {
         isInt = false;
         while (_isDigit()) position++;
       } else {
         position--;  // No digit, backtrack.
@@ skipping 210 matching lines @@
         });
         _sb.add('}');
         _seen.removeLast();
         return;
 
       default:
         throw const JsonUnsupportedObjectType();
     }
   }
 }