MFC r275553, r275612;

MFC	r275553, r275612;

patch(1): Bring fixes from OpenBSD

Check fstat return value.  Use off_t for file size and offsets.
Avoid iterating over end of string.

Introduce strtolinenum to properly check line numbers while parsing:
no signs, no spaces, just digits, 0 <= x <= LONG_MAX

Properly validate line ranges supplied in diff file to prevent overflows.
Also fixes an out of boundary memory access because the resulting values
are used as array indices.

PR:		195436
Obtained from:	OpenBSD

git-svn-id: svn://svn.freebsd.org/base/stable/10@275841 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f