Prevent dropping ellipsis URL

[shuuji3]

Hello, this is a follow-up PR for #585.

I focused on the ellipsis part of the URL in the last PR and missed including the first protocol part like https:// as an invisible text. Without it, Elk still failed to recover the complete URL after saving the edited post (for example, https://takahe.social became a plain text takahe.social).

Now:

[andrewgodwin]

Thanks!