WebGLRenderer: Avoid missing attribute errors. See #11435

src/renderers/WebGLRenderer.js

@@ -951,6 +951,10 @@ function WebGLRenderer( parameters ) {
 
 					var attribute = attributes.get( geometryAttribute );
 
+					// TODO Attribute may not be available on context restore
+
+					if ( attribute === undefined ) continue;
+
 					var buffer = attribute.buffer;
 					var type = attribute.type;
 					var bytesPerElement = attribute.bytesPerElement;