title: 'invalid context error 0x0', when editing uitextfield using mult byte keyboard with iOS 6.0
body: <p>I updated iOS 6.0 SDK with Xcode 4.5.1, and I had invalid context error 0x0 when editing UITextField with mult byte keyboard（e.g. japanese keyboard） in my application.
  The following is error:</p>
  
  <pre><code>Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextSaveGState: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextDrawLinearGradient: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextSetFillColorWithColor: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextFillRects: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextFillRects: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextSetFillColorWithColor: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextFillRects: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextSaveGState: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextDrawLinearGradient: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextSetFillColorWithColor: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextFillRects: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextFillRects: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextSetFillColorWithColor: invalid context 0x0
  Oct  9 21:46:44 example.com Example[2303] &lt;Error&gt;: CGContextFillRects: invalid context 0x0
  </code></pre>
  
  <p>I tried to create new project and I had these errors.
  The following is new project code:</p>
  
  <pre><code>- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
  {
     self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
     // Override point for customization after application launch.
     self.window.backgroundColor = [UIColor whiteColor];
     [self.window makeKeyAndVisible];
  
     UITextField *foo = [[UITextField alloc] initWithFrame:CGRectMake(30, 30, 200, 50)];
  
     [self.window addSubview:foo];
  
     return YES;
  }
  </code></pre>
  
  <p>if you edit with US keyboard, you will not have errors.
  Do you know how to avoid this problem?</p>