When using a bad path over FTP, as in when libcurl couldn't CWD into all

When using a bad path over FTP, as in when libcurl couldn't CWD into all
given subdirs, libcurl would still "remember" the full path as if it is the
current directory libcurl is in so that the next curl_easy_perform() would
get really confused if it tried the same path again - as it would not issue
any CWD commands at all, assuming it is already in the "proper" dir.

Starting now, a failed CWD command sets a flag that prevents the path to be
"remembered" after returning.