call PasswordBoxOnPasswordChanged after initialization
call PasswordBoxOnPasswordChanged after initialization

to support passwordboxes which are initially not empty
fixes #213

tipunch74/MaterialDesignInXamlToolkit,DingpingZhang/MaterialDesignInXamlToolkit,ButchersBoy/MaterialDesignInXamlToolkit,tipunch74/MaterialDesignInXamlToolkit,tipunch74/MaterialDesignInXamlToolkit,ButchersBoy/MaterialDesignInXamlToolkit,ButchersBoy/MaterialDesignInXamlToolkit