MFV: less: Do not trust st_size if it equals zero

This is a smaller version of upstream
1fafd968b48e5cea6c85f126d77071a8de707a55 to address the
issue that less not being able to operate on files
residing in pseudo-filesystems that advertize a zero
size value.

PR: bin/276133

(cherry picked from commit cae336280b0d7ad3d49788c5fc0986f91328eb50)