fix(getRootUrl)!: If not configured use first subdirectory as webroot instead of last

[susnux]

Situation: Webserver configured for path rewrite (remove the index.php):

Before:

• Current path: /nextcloud/apps/files
• Result of getRoot(): /nextcloud/apps

After:

• Current path: /nextcloud/apps/files
• Result of getRoot(): /nextcloud

This affects only situations where the web root is not correctly configured by Nextcloud, but I think we should then only expect the first sub-directory to be the web root instead of all directories.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (3f8327e) 97.53% compared to head (7a2109f) 98.75%.
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #570      +/-   ##
==========================================
+ Coverage   97.53%   98.75%   +1.21%     
==========================================
  Files           1        1              
  Lines         243      240       -3     
  Branches       36       35       -1     
==========================================
  Hits          237      237              
+ Misses          5        1       -4     
- Partials        1        2       +1     

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[Antreesy]

Changes make sense, but I've never tried a webroot configuration, so might miss something important

[Antreesy]

Gave it a test, as close as possible:

• webroot is configured for docker-dev as per issue description: Document using a different webroot juliusknorr/nextcloud-docker-dev#297
• couldn't set htaccess.RewriteBase in config
• window._oc_webroot is set to undefined (NC resolves it automatically even if wasn't configured in config.php)
• used webroot = webroot.replace('/index.php/', '/') (to imitate rewritebase)

Before	After

So far, previous code breaks all requests, which used getRootUrl, if app ever reach this line