Fix dragging after one point already placed incorrectly entering drawing mode

Author: peppy

Diff for: osu.Game.Rulesets.Osu/Edit/Blueprints/Sliders/SliderPlacementBlueprint.cs

@@ -171,7 +171,7 @@ protected override bool OnDragStart(DragStartEvent e)
                 return base.OnDragStart(e);
 
             // Only enter drawing mode if no additional control points have been placed.
-            if (HitObject.Path.ControlPoints.Count > 2)
+            if (HitObject.Path.ControlPoints.Count > 2 || HitObject.Path.ControlPoints.Last() != cursor)
                 return base.OnDragStart(e);
 
             bSplineBuilder.AddLinearPoint(ToLocalSpace(e.ScreenSpaceMouseDownPosition) - HitObject.Position);