Fix crash with StaticMoverWithLiftSpeed

Fixed by max480 in their own repository, max4805/MaxHelpingHand

Author: catapillie

source/Misc/StaticMoverWithLiftSpeed.cs

@@ -1,18 +1,21 @@
 using Microsoft.Xna.Framework;
 using Monocle;
 using System;
+using System.Collections.Generic;
 
 namespace Celeste.Mod.VortexHelper.Misc {
     /// <summary>
     /// A static mover that has an extra "event" OnSetLiftSpeed that is called with the exact value of the lift speed just before any move.
     /// This allows to attach solids to solids with both solids having the same lift speed.
+    /// <para/>
+    /// <see href="https://github.com/max4805/MaxHelpingHand/blob/e76ac4ca2b06869f80f7dca82f231f4709a5aeb2/Entities/StaticMoverWithLiftSpeed.cs">Originally implemented by max480 in MaxHelpingHand.</see>
     /// </summary>
     [TrackedAs(typeof(StaticMover))]
     public class StaticMoverWithLiftSpeed : StaticMover {
         public Action<Vector2> OnSetLiftSpeed;
 
         public static class Hooks {
-            private static Platform currentPlatform;
+            private static LinkedList<Platform> currentPlatforms = new();
 
             public static void Hook() {
                 On.Celeste.Platform.MoveStaticMovers += Platform_MoveStaticMovers;
@@ -25,14 +28,14 @@ public static void Unhook() {
             }
 
             private static void Platform_MoveStaticMovers(On.Celeste.Platform.orig_MoveStaticMovers orig, Platform self, Vector2 amount) {
-                currentPlatform = self;
+                currentPlatforms.AddLast(self);
                 orig(self, amount);
-                currentPlatform = null;
+                currentPlatforms.RemoveLast();
             }
 
             private static void StaticMover_Move(On.Celeste.StaticMover.orig_Move orig, StaticMover self, Vector2 amount) {
                 if (self is StaticMoverWithLiftSpeed staticMover) {
-                    staticMover.OnSetLiftSpeed?.Invoke(currentPlatform.LiftSpeed);
+                    staticMover.OnSetLiftSpeed?.Invoke(currentPlatforms.Last.Value.LiftSpeed);
                 }
 
                 orig(self, amount);