message: Fix when webgl2 is not exist on global scope
diff: @@ -292,7 +292,7 @@ export class ContextSystem extends System
  }
  const hasuint32
  - = (gl instanceof WebGL2RenderingContext)
  + = ('WebGL2RenderingContext' in window && gl instanceof window.WebGL2RenderingContext)
  || !!(gl as WebGLRenderingContext).getExtension('OES_element_index_uint');
  this.supports.uint32Indices = hasuint32;
  