Normalize the behavior between the file functions and those on
SplFileObject.
Be consistent about throwing regardless of whether the delimiter etc
is empty or has too many characters. I don't think it's worthwhile
to distinguish these cases.
Back when we looked into this originally, there was some hope that
we might want to add support for multiple-character delimiter etc,
but after a cursory look, I really don't think this is going to
happen (for fputcsv maybe, but for fgetcsv this just makes an already
broken function much more complicated.)
Closes GH-6188.