There seems to be a bug with `file-name-case-insensitive-p` when given a
file name that doesn't exist and does not have a root that exists. For
instance `(file-name-case-insensitive-p "some/project")`.

Unfortunately I'm unable to give a simple reproduction as this only
seemed to happen when running tests for CIDER under cask. This behavior
seems to have been introduced in
81d6418e6b7c3e637dccf9c856d9c4b94bd43b97 with the commit message:

Fix file-name-case-insensitive-p on non-existent files

* src/fileio.c (Ffile_name_case_insensitive_p): If the file
doesn't exist, move up the filesystem tree until an existing
directory is found.  Then test that directory for
case-insensitivity.  (Bug#32246)

https://github.com/clojure-emacs/cider/pull/2669/commits/2039abd3c48214200a9e50a5288246011d48eb3e

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