LibWeb: Fix floating boxes getting stacked on top of each other

This was caused by the freestanding margin_box_rect() using 0 for the
content height instead of the actual content height.

Userland/Libraries/LibWeb/Layout/FormattingState.cpp

@@ -40,7 +40,7 @@ void FormattingState::commit()
 Gfx::FloatRect margin_box_rect(Box const& box, FormattingState const& state)
 {
  auto const& box_state = state.get(box);
- auto rect = Gfx::FloatRect { box_state.offset, { box_state.content_width, 0 } };
+ auto rect = Gfx::FloatRect { box_state.offset, { box_state.content_width, box_state.content_height } };
  rect.set_x(rect.x() - box_state.margin_box_left());
  rect.set_width(rect.width() + box_state.margin_box_left() + box_state.margin_box_right());
  rect.set_y(rect.y() - box_state.margin_box_top());