MFC r254338:
Don't send uninitialized memory (two instances of 4 bytes) in
every cookie on the wire. This bug was reported in
https://bugzilla.mozilla.org/show_bug.cgi?id=905080
MFC: r254091

According to POSIX \ in the fnmatch(3) pattern should escape
any character including '\0', but our version replace escaped '\0'
with '\\'.
I.e. fnmatch("\\", "\\", 0) should not match while fnmatch("\\", "", 0)
should (Linux and NetBSD does the same). Was vice versa.

PR:     181129