patch 9.2.0698: [security]: Out-of-bounds write with soundfold()

patch 9.2.0698: [security]: Out-of-bounds write with soundfold()

Problem:  [security]: Out-of-bounds write with soundfold()
          (cipher-creator)
Solution: Add an abort condition to the for loop to validate the buffer
          size.

Github Security Advisory:
https://github.com/vim/vim/security/advisories/GHSA-q8mh-6qm3-25g4

Supported by AI

Signed-off-by: Christian Brabandt <cb@256bit.org>