Make is_file() and friends return false when path contains 0-byte

Make is_file() and friends return false when path contains 0-byte

These functions now return false silently:
is_writable, is_readable, is_executable, is_file, is_dir, is_link,
file_exists

These functions now throw a warning an return false (rather than
throwing a ValueError):
fileperms, fileinode, filesize, fileowner, filegroup, filetype,
fileatime, filemtime, filectime, lstat, stat

See also https://externals.io/message/112333.

Closes GH-6478.