Make the "fetchattr_soft" macro tolerate if the value of the given attribute is None.
Make the "fetchattr_soft" macro tolerate if the value of the given attribute is None.

This fixes the issue that returning an instance created by os.stat_result()
from the "getattr" method caused EINVAL. Issue was reported by Forest Bond.

libfuse/python-fuse,ajnelson/fuse-python,ajnelson/fuse-python,libfuse/python-fuse,ajnelson/fuse-python