[TASK] Sanitize identifiers created client side

[lolli42]

Affects createFolderAction(), fileExistsAction(), fileUploadAction()

[juergen-venne]

– using identifier of existing file returns the expected file entity, as expected.
but
– using the same identifier with storage id changed to a non existent storage 2: the returned JSON is 200: {"state": 1}
– using the same identifier with changed foldername to a non-existing folder the returned JSON is 200: {"state": 1}
– using identifier of non existing file returns 200:{"state": 0}
Is that the expected behavior?

[lolli42]

@juergen-venne yes. the api does not throw different error messages between 'no such storage' and 'no such folder'. there is no need to change this until it is really needed.