SystemMenu: Fix bad behavior in shutdown dialog

The selected option was stored in a captured stack variable which was
long gone by the time we looked at it, so this dialog didn't really
behave the way you'd expect. Put it in a member instead. :^)

Applications/SystemMenu/PowerDialog.cpp

@@ -82,20 +82,19 @@ PowerDialog::PowerDialog()
  header->set_size_policy(GUI::SizePolicy::Fill, GUI::SizePolicy::Fixed);
  header->set_font(Gfx::Font::default_bold_font());
 
- int selected = -1;
  for (size_t i = 0; i < options.size(); i++) {
  auto action = options[i];
  auto radio = main->add<GUI::RadioButton>();
  radio->set_enabled(action.enabled);
  radio->set_text(action.title);
 
- radio->on_checked = [&selected, i](auto) {
- selected = i;
+ radio->on_checked = [this, i](auto) {
+ m_selected_option = i;
  };
 
  if (action.default_action) {
  radio->set_checked(true);
- selected = i;
+ m_selected_option = i;
  }
  }
 
@@ -104,8 +103,8 @@ PowerDialog::PowerDialog()
  button_box->layout()->set_spacing(8);
 
  auto ok_button = button_box->add<GUI::Button>();
- ok_button->on_click = [this, &selected](auto&) {
- done(selected);
+ ok_button->on_click = [this](auto&) {
+ done(m_selected_option);
  };
  ok_button->set_text("OK");
 

Applications/SystemMenu/PowerDialog.h

@@ -36,4 +36,6 @@ class PowerDialog : public GUI::Dialog {
 private:
  PowerDialog();
  ~PowerDialog();
+
+ int m_selected_option { -1 };
 };