fix crash when reloading inside dream block

Celeste.Mod.mm/Patches/Dust.cs

@@ -1,4 +1,10 @@
-using Microsoft.Xna.Framework;
+using System;
+using Celeste;
+using Microsoft.Xna.Framework;
+using Mono.Cecil;
+using Monocle;
+using MonoMod;
+using MonoMod.Cil;
 
 namespace Celeste {
     // Dust is static.
@@ -7,5 +13,45 @@ class patch_Dust {
         public static void Burst(Vector2 position, float direction, int count = 1) {
             Dust.Burst(position, direction, count, null);
         }
+
+        [MonoModIgnore]
+        [PatchDustBurst]
+        public static extern void Burst(Vector2 position, float direction, int count, ParticleType particleType);
+
+        [MonoModIgnore]
+        [PatchDustBurst]
+        public static extern void BurstFG(Vector2 position, float direction, int count, float range, ParticleType particleType);
+
     }
 }
+
+namespace MonoMod {
+
+    /// <summary>
+    /// Add an early return if Engine.Scene is not a Level, to avoid a crash.
+    /// </summary>
+    [MonoModCustomMethodAttribute(nameof(MonoModRules.PatchDustBurst))]
+    class PatchDustBurstAttribute : Attribute {}
+
+    static partial class MonoModRules {
+
+        public static void PatchDustBurst(ILContext context, CustomAttribute attrib) {
+            ILCursor cursor = new ILCursor(context);
+
+            ILLabel beforeRet = cursor.DefineLabel();
+            int loc = -1;
+
+            cursor.GotoNext(MoveType.After,
+                            instr => instr.MatchIsinst(out var _),
+                            instr => instr.MatchStloc(out loc));
+            cursor.EmitLdloc(loc);
+            cursor.EmitBrfalse(beforeRet);
+
+            cursor.GotoNext(MoveType.Before,
+                            instr => instr.MatchRet());
+            cursor.MarkLabel(beforeRet);
+        }
+
+    }
+
+}