Links in file lists in theme/plugin editors don't work in network admin

[westonruter]

On multisite, clicking on a link in the theme/plugin file trees results in the default file for the theme or plugin to always be loaded. The reason for this is that in 4.9 the admin_url() function is being used and so when the user visits /wp-admin/theme-editor.php?... they get redirected to the network admin but without the query params.

Introduced in [41721] for #24048.

Reported by @obenland in ​https://wordpress.slack.com/archives/C0381N237/p1509639301000776

Video of issue: ​https://wordpress.slack.com/files/U02RPUBDZ/F7TBQSNTA/multisite-editors.mov

[westonruter]

4.8.3 just has theme-editor.php?… as the URL without any path: ​https://github.com/WordPress/wordpress-develop/blob/32f78b0ff7c10654058f5572917548253c6492fc/src/wp-admin/theme-editor.php#L246

Whereas in 4.9 there is the wp_print_theme_file_tree() function which does admin_url( 'theme-editor.php' ): ​https://github.com/WordPress/wordpress-develop/blob/d6aece2a336225e239798e99f163b30e2e9d8874/src/wp-admin/includes/misc.php#L336

42420.0.diff​ merely replaces admin_url( 'theme-editor.php' ) with theme-editor.php, and similarly for the plugin editor.

[flixos90]

I'd suggest going with self_admin_url() which will ensure the correct admin URL is used. I used that in 42420.diff​.

[obenland]

I like @flixos90 approach in 42420.diff​. 👍

[westonruter]

I do too. @obenland commit?

[obenland]

In 42115:

File Editors: Account for network admin use

Fixes a bug where files couldn't be accessed in multisite installs.

Props flixos90, westonruter.
Fixes #42420.