Solitaire: Make sure to not add card twice to m_focused_cards

There is a possibility that the same card gets added twice to
m_focused_cards when first mousedown_event fires and then
doubleclick_event, without the cards redrawing first. This would cause
mouseup_event to try to pop too many cards from the stack, causing an
assertion to fail.

When the system is laggy there is also a high possibility that
mousedown_event would fire twice without redrawing the cards first,
causing another assertion to fail. Addditional mousedown_events will
just be ignored now.

Games/Solitaire/SolitaireWidget.cpp

@@ -212,7 +212,7 @@ void SolitaireWidget::mousedown_event(GUI::MouseEvent& event)
  update_score(5);
  m_has_to_repaint = true;
  }
- } else {
+ } else if (m_focused_cards.is_empty()) {
  to_check.add_all_grabbed_cards(click_location, m_focused_cards);
  m_mouse_down_location = click_location;
  to_check.set_focused(true);
@@ -313,8 +313,10 @@ void SolitaireWidget::doubleclick_event(GUI::MouseEvent& event)
  return;
  }
 
- auto click_location = event.position();
+ if (!m_focused_cards.is_empty())
+ return;
 
+ auto click_location = event.position();
  for (auto& to_check : m_stacks) {
  if (to_check.type() == CardStack::Type::Foundation)
  continue;