See https://github.com/jrsoftware/issrc/commit/3ee150d87904306baeed2468af94b4ddd802adf3#commitcomment-2418559, reverted: Use PathCombine for if DestName starts with a slash (PathDrivePartLengthEx doesn't always leave of the trailing slash). (reverse-merged from commit 3ee150d87904306baeed2468af94b4ddd802adf3)