Fix URL calculation in clone input box (#29470)

Ported the function as-is and added comments so we don't forget about
this in the future.

Fixes: https://github.com/go-gitea/gitea/issues/29462

web_src/js/webcomponents/GiteaOriginUrl.js

@@ -1,7 +1,8 @@
-// Convert an absolute or relative URL to an absolute URL with the current origin
+// Convert an absolute or relative URL to an absolute URL with the current origin. It only
+// processes absolute HTTP/HTTPS URLs or relative URLs like '/xxx' or '//host/xxx'.
+// NOTE: Keep this function in sync with clone_script.tmpl
 export function toOriginUrl(urlStr) {
   try {
-    // only process absolute HTTP/HTTPS URL or relative URLs ('/xxx' or '//host/xxx')
     if (urlStr.startsWith('http://') || urlStr.startsWith('https://') || urlStr.startsWith('/')) {
       const {origin, protocol, hostname, port} = window.location;
       const url = new URL(urlStr, origin);