check for directory using DAV:iscollection

[miklcct]

The current check for directory, which thinks an item is a directory if the content-length is empty of 0, is error-prone and fails on my IIS server where the client returns a string "0" for directories. It may also fail if there is an empty file in the directory.

This fix properly checks for a directory using DAV:iscollection.

[Teods]

This PR is waiting for ages, could you please validate and merge it ?

It will fix the bug of the "has" function who return "true" for whatever you write has path because the normalize function always return an non-empty array who pass the (bool) check.