fix references check in ext_instance_features

src/SharpGLTF.Cesium/Schema2/Ext.InstanceFeatures.cs

@@ -38,13 +38,13 @@ namespace SharpGLTF.Schema2
                     var gpuInstancing = _node.GetGpuInstancing();
                     var featureIdAccessors = gpuInstancing.GetAccessor(expectedVertexAttribute);
                     Guard.NotNull(featureIdAccessors, expectedVertexAttribute);
+                }
 
-                    if (instanceFeatureId.PropertyTable.HasValue)
-                    {
-                        var metadataExtension = _node.LogicalParent.GetExtension<EXTStructuralMetadataRoot>();
-                        Guard.NotNull(metadataExtension, nameof(metadataExtension), "EXT_Structural_Metadata extension is not found.");
-                        Guard.NotNull(metadataExtension.PropertyTables[instanceFeatureId.PropertyTable.Value], nameof(instanceFeatureId.PropertyTable), $"Property table index {instanceFeatureId.PropertyTable.Value} does not exist");
-                    }
+                if (instanceFeatureId.PropertyTable.HasValue)
+                {
+                    var metadataExtension = _node.LogicalParent.GetExtension<EXTStructuralMetadataRoot>();
+                    Guard.NotNull(metadataExtension, nameof(metadataExtension), "EXT_Structural_Metadata extension is not found.");
+                    Guard.NotNull(metadataExtension.PropertyTables[instanceFeatureId.PropertyTable.Value], nameof(instanceFeatureId.PropertyTable), $"Property table index {instanceFeatureId.PropertyTable.Value} does not exist");
                 }
             }