Fixed PreIntegratedFGD texture being destroyed in some cases and not re-rendered correctly (also removed some redundant tests in Lit.cs and StackLit.cs)

com.unity.render-pipelines.high-definition/HDRP/Material/Lit/Lit.cs

         // Init precomputed texture
         //-----------------------------------------------------------------------------
 
-        bool m_isInit;
-
         public Lit() {}
 
         public override void Build(HDRenderPipelineAsset hdAsset)
-
-            m_isInit = false;
         }
 
         public override void Cleanup()
-
-            m_isInit = false;
-            if (m_isInit)
-                return;
-
-
-            m_isInit = true;
         }
 
         public override void Bind()

com.unity.render-pipelines.high-definition/HDRP/Material/PreIntegratedFGD/PreIntegratedFGD.cs

 
         public void RenderInit(FGDIndex index, CommandBuffer cmd)
         {
-            if (m_isInit[(int)index])
+            // Here we have to test IsCreated because in some circumstances (like loading RenderDoc), the texture is internally destroyed but we don't know from C# side.
+            // In this case IsCreated will return false, allowing us to re-render the texture (setting the texture as current RT during DrawFullScreen will automatically re-create it internally)
+            if (m_isInit[(int)index] && m_PreIntegratedFGD[(int)index].IsCreated())
                 return;
 
             using (new ProfilingSample(cmd, "PreIntegratedFGD Material Generation"))

com.unity.render-pipelines.high-definition/HDRP/Material/StackLit/StackLit.cs

         // Init precomputed textures
         //-----------------------------------------------------------------------------
 
-        bool m_isInit;
-
         public StackLit() {}
 
         public override void Build(HDRenderPipelineAsset hdAsset)
-
-            m_isInit = false;
         }
 
         public override void Cleanup()
-
-            m_isInit = false;
-            if (m_isInit)
-                return;
-
-
-            m_isInit = true;
         }
 
         public override void Bind()