Fix for CORS issue

I was having problems using Elementor to edit domain-mapped pages … and the standard CORS fix did not work for me.

I made a small edit to the plugin to fix the issue without the need to change server settings, which has the benefit of not reducing the security of the website…

In function falke_mdm_replace_landingurl, wrap the foreach with if is_admin() { ... }

That way the plugin only tries to change the URL of a domain-mapped page if the function is being called from the front-end. That may not be the best way to accomplish that, but it does make sense to me. I would love to see this change, or something similar, in the next version of the plugin.