Fix FTP response parsing and error handling memory leaks (#2133)

Fix FTP response parsing and error handling memory leaks (#2133)

FTP EPLF parsing leaks in ftpListParseParts() were detected by Coverity.
CID 1660782 and CID 1660785: Resource leaks (RESOURCE_LEAK).

Three other FTP client-related leaks were detected by Valgrind:

* Ftp::CtrlChannel::last_reply
* ErrorPage::ftp::cwd_msg
* Ftp::DataChannel::host