TEST: skip POSIX errcode zero in tesst/recipes/02-test_errstr.t

TEST: skip POSIX errcode zero in tesst/recipes/02-test_errstr.t

On most systems, there is no E macro for errcode zero in <errno.h>,
which means that it seldom comes up here.  However, reports indicate
that some platforms do have an E macro for errcode zero.
With perl, errcode zero is a bit special.  Perl consistently gives
the empty string for that one, while the C strerror() may give back
something else.  The easiest way to deal with that possible mismatch
is to skip this errcode.

Fixes #12798

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/12799)