Requesting backport of read_key_file memory leak fix to 2.4

[NIIBE Yutaka]

Hello,

Sorah Fukumori wrote:
> This bug can be reproduced on 2.4.8, and I'd like to get it fixed on
> 2.4 before it reaches EOL.

Sorry, I should have done earlier.  Ahyhow, applied and pushed to
2.4 branch.
--