Unable to separate runtime from installation

[pilophae]

Describe the bug
I install Snappymail to /usr/share/snappymail using AUR in Archlinux. In order to keep runtime data in my web server directory /srv/http I then symlink all files from the installation directory except index.php and include.php which are manually copied.

This broke with commit 538f752 where it is assumed that APP_INDEX_ROOT_PATH and APP_VERSION_ROOT_PATH share a parent path, which they do not do for me. This means that the absolute path is used for resources, such as JS or CSS.

This is what my "variables" look like:

APP_INDEX_ROOT_PATH=/srv/http/mail.ayeon.org/htdocs/
APP_VERSION_ROOT_PATH=/usr/share/snappymail/snappymail/v/2.21.2/

To Reproduce

1. Place index.php in some other directory than the installation directory.
2. Symlink the other files to the same directory.

Expected behavior
The relative path to resources should be used when rendering HTML.

Please complete the following information:

• Browser: N/A
• IMAP daemon: N/A
• PHP version: 8.1.12
• SnappyMail Version: 2.21.2