Return the value of #WebKitPrintCustomWidget:widget property for the given
@print_custom_widget object. The returned value will always be valid if called
from #WebKitPrintCustomWidget::apply or #WebKitPrintCustomWidget::update
callbacks, but it will be %NULL if called after the
#WebKitPrintCustomWidget::apply signal is emitted.
Return the value of #WebKitPrintCustomWidget:widget property for the given @print_custom_widget object. The returned value will always be valid if called from #WebKitPrintCustomWidget::apply or #WebKitPrintCustomWidget::update callbacks, but it will be %NULL if called after the #WebKitPrintCustomWidget::apply signal is emitted.