Commit
02c5631 (difftool --dir-diff: symlink all files matching the
working tree, 2013-03-14) does not handle the case where a file that is
being compared does not exist in the working tree. Fix this by checking
for existence explicitly before running git-hash-object.
Reported-by: Kevin Bracey <kevin@bracey.fi>
Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>