libc/_collate_lookup: Fix segfault seen on ISO-8859-5 locales
The fix for the Russian collation issue seemed to have bug in it.
Segfault was discovered by Lauri Tirkkonen of Illumos and confirmed by
Bapt@FreeBSD.org. Lauri suggested this as a fix, but as of this writing
Bapt hasn't confirmed that this is final solution for FreeBSD. Due to
personal reasons, I cannot wait for this confirmation longer. I believe
this fix is better than what is currently in place, even if it is not
the final solution.