Fix visitDependents_impl on some asset

Author: kevyuu

include/nbl/asset/ICPUAccelerationStructure.h

@@ -362,6 +362,7 @@ class ICPUTopLevelAccelerationStructure final : public IAsset, public ITopLevelA
 
 		inline virtual void visitDependents_impl(std::function<bool(const IAsset*)> visit) const override
     {
+        if (!m_instances) return;
         for (const auto& instance : *m_instances)
             if (!visit(instance.getBase().blas.get())) return;
     }

include/nbl/asset/ICPUDescriptorSetLayout.h

@@ -65,7 +65,7 @@ class ICPUDescriptorSetLayout : public IDescriptorSetLayout<ICPUSampler>, public
 
       inline virtual void visitDependents_impl(std::function<bool(const IAsset*)> visit) const override
       {
-          if (m_immutableSamplers) return;
+          if (!m_immutableSamplers) return;
           for (const auto& sampler : *m_immutableSamplers)
               if (!visit(sampler.get())) return;
       }

include/nbl/asset/ICPUPipelineLayout.h

@@ -66,14 +66,24 @@ class ICPUPipelineLayout : public IAsset, public IPipelineLayout<ICPUDescriptorS
         static inline constexpr auto AssetType = ET_PIPELINE_LAYOUT;
         inline E_TYPE getAssetType() const override { return AssetType; }
 
+        inline virtual bool valid() const override
+        {
+            for (auto i = 0; i < m_descSetLayouts.size(); i++)
+            {
+                if (!m_descSetLayouts[i]) continue;
+                if (!m_descSetLayouts[i]->valid()) return false;
+            }
+            return true;
+        }
+
     protected:
 		virtual ~ICPUPipelineLayout() = default;
 
       inline virtual void visitDependents_impl(std::function<bool(const IAsset*)> visit) const override
       {
           for (auto i = 0; i < m_descSetLayouts.size(); i++)
           {
-              if (m_descSetLayouts[i]) continue;
+              if (!m_descSetLayouts[i]) continue;
               if (!visit(m_descSetLayouts[i].get())) return;
           }
       }