Handle ENOTDIR errno in Path::exists()

[TryExceptElse]

Previously, Path::exists() would produce an exception when a parent of the checked path existed, but was not a directory (for example: if the user called Path("foo/baz.txt").exists() when "foo" was a file).

This change makes Pathie act similarly to path libraries such as Python's pathlib, which returns false given the same inputs.