fix: explicit undefined check in header transclude

Jacky Zhao

2023-11-19 516d9a27e7e2c08efdf24857b03f1831dbaf7da7

 quartz/plugins/emitters/index.ts

@@ -7,3 +7,4 @@
export { Static } from "./static"
export { ComponentResources } from "./componentResources"
export { NotFoundPage } from "./404"
export { CNAME } from "./cname"