mmap() will fail for a zero-length mapping. A valid object should still
be returned to signal that the file was opened to the caller but it
should have a nullptr for data and zero for size.
Signed-off-by: Rick Altherr <kc8apf@kc8apf.net>
Signed-off-by: Tim 'mithro' Ansell <mithro@mithis.com>