Make handling of NULL bytes in file paths more consistent (WIP)

Not all extensions consistently throw exceptions when the user passes
a path name containing null bytes. Also, some extens

Make handling of NULL bytes in file paths more consistent (WIP)

Not all extensions consistently throw exceptions when the user passes
a path name containing null bytes. Also, some extensions would throw
a ValueError while others would throw a TypeError. Error messages
also varied.

Now a ValueError is thrown after all failed path checks, at least for
as far as these occur in functions that are exposed to userland.

Closes GH-6216.

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