SvnLoaderFromRemoteDump: Fix not_found visit status for non first visit
When a subversion origin no longer exists since its last visit, SvnLoaderFromRemoteDump was not setting visit status to "not_found" but to "failed. So ensure to set correct visit status when encountering such cases.
Fixes SWH-LOADER-SVN-7A.
Migrated from D7619 (view on Phabricator)