The prefix/postfix change is a red herring, that doesn't do anything (since the expression result isn't used). Which means that the security fix is interspersed with code style changes. Maybe there's a reason to do this here, but it's often not considered good practice because it makes it harder to review the code.

AFAICT, the only real changes are in (new) line 411, resetting the cp variable after the loop, and line 416, ignoring write errors. The former is probably the relevant one.