Fix for #3049

This is using inline JS, as this seems to be allowed by the current security policies. But in the first place, it tries to convince Apache to prefer `index.php` over `index.html`, as a remedy for #3049.

I did not find a place where this could cause harm (e.g. where an `index.html` is located as a safety net to ensure a certain directory cannot be listed, and this directory allows user-writeable content. Please double-check.

@DeepDiver1975 @LukasReschke