LibGUI: Callback with the clamped value of Sliders on a jump to cursor

Author: https://github.com/Zaggy1024
Commit: 0c230f5ff0
Pull-request: https://github.com/SerenityOS/serenity/pull/17447

Userland/Libraries/LibGUI/Slider.cpp

@@ -104,7 +104,7 @@ void Slider::mousedown_event(MouseEvent& event)
             start_drag(event.position());
             // Delay the callback to make it aware that a drag has started.
             if (on_change)
-                on_change(new_value);
+                on_change(value());
             return;
         }