Problem: buffer-overflow in do_search() with 'rightleft'
(SuyueGuo)
Solution: after reversing the text (which allocates a new buffer),
re-calculate the text length
Github Advisory:
https://github.com/vim/vim/security/advisories/GHSA-v2x2-cjcg-f9jmcacb6693c1
Add missing change from patch 8.1.1270.
Omit `call delete('Untitled')`: moved again in patch 9.1.0695.
Co-authored-by: Christian Brabandt <cb@256bit.org>
