Fix quick-deleting unselected slider path control point also deleting…

… all selected control points

Closes ppy#31308.

Logic matches corresponding quick-delete logic in
https://github.com/ppy/osu/blob/130802e48048c134c6c8f19c77e3e032834acf72/osu.Game/Screens/Edit/Compose/Components/SelectionHandler.cs#L307-L316.

osu.Game.Rulesets.Osu/Edit/Blueprints/Sliders/Components/PathControlPointVisualiser.cs

@@ -137,23 +137,34 @@ public void SetSelectionTo(PathControlPoint pathControlPoint)
         /// <summary>
         /// Delete all visually selected <see cref="PathControlPoint"/>s.
         /// </summary>
-        /// <returns></returns>
+        /// <returns>Whether any change actually took place.</returns>
         public bool DeleteSelected()
         {
             List<PathControlPoint> toRemove = Pieces.Where(p => p.IsSelected.Value).Select(p => p.ControlPoint).ToList();
 
+            if (!Delete(toRemove))
+                return false;
+
+            // Since pieces are re-used, they will not point to the deleted control points while remaining selected
+            foreach (var piece in Pieces)
+                piece.IsSelected.Value = false;
+
+            return true;
+        }
+
+        /// <summary>
+        /// Delete the specified <see cref="PathControlPoint"/>s.
+        /// </summary>
+        /// <returns>Whether any change actually took place.</returns>
+        public bool Delete(List<PathControlPoint> toRemove)
+        {
             // Ensure that there are any points to be deleted
             if (toRemove.Count == 0)
                 return false;
 
             changeHandler?.BeginChange();
             RemoveControlPointsRequested?.Invoke(toRemove);
             changeHandler?.EndChange();
-
-            // Since pieces are re-used, they will not point to the deleted control points while remaining selected
-            foreach (var piece in Pieces)
-                piece.IsSelected.Value = false;
-
             return true;
         }
 

osu.Game.Rulesets.Osu/Edit/Blueprints/Sliders/SliderSelectionBlueprint.cs

@@ -140,8 +140,11 @@ public override bool HandleQuickDeletion()
             if (hoveredControlPoint == null)
                 return false;
 
-            hoveredControlPoint.IsSelected.Value = true;
-            ControlPointVisualiser?.DeleteSelected();
+            if (hoveredControlPoint.IsSelected.Value)
+                ControlPointVisualiser?.DeleteSelected();
+            else
+                ControlPointVisualiser?.Delete([hoveredControlPoint.ControlPoint]);
+
             return true;
         }