Bug 1804829 - Avoid last use of location.hostname on about:neterror page. r=prathiksha

It looks like hostname is sometimes undefined, which triggers a Fluent error.
The HOST_NAME is determined from location.href,
and falls back to an empty string value about which Fluent is much happier.

Differential Revision: https://phabricator.services.mozilla.com/D164538

toolkit/content/aboutNetError.mjs

@@ -308,7 +308,7 @@ function initPage() {
       document.getElementById("errorShortDesc").hidden = true;
 
       document.l10n.setAttributes(longDesc, "csp-xfo-blocked-long-desc", {
-        hostname: document.location.hostname ?? "", // FIXME - should this be HOST_NAME?
+        hostname: HOST_NAME,
       });
       longDesc = null;