fix: explicit undefined check in header transclude

Jacky Zhao

2023-11-19 516d9a27e7e2c08efdf24857b03f1831dbaf7da7

 quartz/components/Explorer.tsx

@@ -86,7 +86,7 @@
  function Explorer({ allFiles, displayClass, fileData }: QuartzComponentProps) {
    constructFileTree(allFiles)
    return (
      <div class={`explorer ${displayClass}`}>
      <div class={`explorer ${displayClass ?? ""}`}>
        <button
          type="button"
          id="explorer"