LibGUI: Make ScrollBar show hover state of scrubber after gutter drag

With this, if clicking the gutter until the scrubber's below the
mouse and then releasing the mouse, the scrubber is correctly
highlighted after releasing the mouse.

Libraries/LibGUI/ScrollBar.cpp

@@ -275,6 +275,7 @@ void ScrollBar::on_automatic_scrolling_timer_fired()
     }
     if (m_pressed_component == Component::Gutter && component_at_position(m_last_mouse_position) == Component::Gutter) {
         scroll_by_page(m_last_mouse_position);
+        m_hovered_component = component_at_position(m_last_mouse_position);
         return;
     }
 }