script/serve-public.js: handle all URLs ending in a slash correctly

There is already code to handle the top-level URL correctly. However,
URLs like http://localhost:5000/book/ still weren't handled by appending
`index.html`. Let's fix this.

This is needed because we are _just_ about to add tests to verify that
the book redirects at URLs like https://git-scm.com/book/ work.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

script/serve-public.js

@@ -25,7 +25,14 @@ const mimeTypes = {
 
 const handler = (request, response) => {
     const pathname = decodeURIComponent(url.parse(request.url).pathname);
-    let filename = path.join(basePath, pathname === "/" ? "index.html" : pathname);
+    let filename = path.join(
+        basePath,
+        pathname === "/"
+        ? "index.html"
+        : pathname.endsWith("/")
+          ? `${pathname}index.html`
+          : pathname
+    );
 
     let stats = fs.statSync(filename, { throwIfNoEntry: false });
     if (!stats?.isFile() && !filename.match(/\.[A-Za-z0-9]{1,11}$/)) {