WP_Filesyste: SSH2 PHP Extension support: Fix a case where defining a custom FS_CHMOD_FILE / FS_CHMOD_DIR constant wouldn't take effect due to chmod() failing with a invalid path. Fixes #23589


git-svn-id: https://develop.svn.wordpress.org/trunk@25306 602fd350-edb4-49c9-b593-d223f7449a82