WP_Filesystem: PemFTP: Detect dl() being disabled in order to avoid any fatals...

WP_Filesystem: PemFTP: Detect dl() being disabled in order to avoid any fatals which may be produced when the Sockets extension is not available. Props to kurtpayne for initial patch, Fixes #20187


git-svn-id: https://core.svn.wordpress.org/trunk@20311 1a063a9b-81f0-0310-95a4-ce76da25c4cd