Fixed issue that was causing Lightweight pipeline to not be disposed/recreated when changing asset settings.

Assets/ScriptableRenderPipeline/LightweightPipeline/LightweightPipeline.cs

 
         public override void Dispose()
         {
+            base.Dispose();
+
             Shader.globalRenderPipeline = "";
             if (m_LightIndexListBuffer != null)
             {

Assets/ScriptableRenderPipeline/LightweightPipeline/LightweightPipelineAsset.cs

             return new LightweightPipeline(this);
         }
 
+        void OnValidate()
+        {
+            DestroyCreatedInstances();
+        }
+
         #region PipelineAssetSettings
 
         [SerializeField] private int m_MaxPixelLights = 1;