Fix crash in particles system when assets gets loading/unloaded while async jobs are active

Source/Engine/Particles/Particles.h

@@ -3,6 +3,7 @@
 #pragma once
 
 #include "Engine/Scripting/ScriptingType.h"
+#include "Engine/Threading/ConcurrentSystemLocker.h"
 
 class TaskGraphSystem;
 struct RenderContext;
@@ -27,6 +28,9 @@ API_CLASS(Static) class FLAXENGINE_API Particles
     /// </summary>
     API_FIELD(ReadOnly) static TaskGraphSystem* System;
 
+    // Data access locker for animations data.
+    static ConcurrentSystemLocker SystemLocker;
+
 public:
     /// <summary>
     /// Updates the effect during next particles simulation tick.