UITextField 明暗文坐标显示优化

- (IBAction)openEyes:(UIButton *)sender {
    sender.selected = !sender.selected;
    //密文明文更换时候的出现空格 或者光标错乱
    NSString *text = self.passwordTextField.text;
    self.passwordTextField.text = @"";
    self.passwordTextField.secureTextEntry = !sender.selected;
    self.passwordTextField.text = text;
}