diff: Report I/O errors in Stone algorithmstable/14

In the legacy Stone algorithm, we do a first pass over the files to
check if they're identical before we start diffing them.  That code
would correctly set the exit status if an I/O error was encountered,
but would not emit an error message.  Do so.

PR:		292198
MFC after:	1 week
Sponsored by:	Klara, Inc.
Reviewed by:	thj
Differential Revision:	https://reviews.freebsd.org/D55125

(cherry picked from commit f8c12e6e3874cdd353fb16785da6f4e7eb134cd9)

0 files changed, 0 insertions, 0 deletions