fix(Node): Handle slash as root path for public webdav endpoint

[susnux]

dirname and path both depend on the root property, but in case of the webdav endpoint the root is just / so in this case we need to remove the remote URL part first before we remove the root.

before	after
source: http://foo.com/public.php/webdav/bar root: / path: /foo.com/public.php/webdav/bar	source: http://foo.com/public.php/webdav/bar root: / path: /bar

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2feb511) 77.33% compared to head (a5c7260) 77.75%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #847      +/-   ##
==========================================
+ Coverage   77.33%   77.75%   +0.41%     
==========================================
  Files          17       17              
  Lines         428      436       +8     
  Branches      113      115       +2     
==========================================
+ Hits          331      339       +8     
  Misses         97       97              

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