When `ftp_nlist()` receives an empty path, it checks the current working directory and may return `true`.
This affects:
* `WP_Filesystem_FTPext::exists()`
* `WP_Filesystem_ftpsockets::exists()`
As the purpose of the API is to provide a consistent interface for various filesystem implementations, this commit updates the affected methods to returns `false` when an empty path is provided, bringing consistency with the other filesystem abstraction classes, specifically `WP_Filesystem_Direct` and `WP_Filesystem_SSH2`.
Follow-up to [6779], [11821], [25274], [31815].
Props mkox, costdev, Zdrobau, dd32, pbiron, azaozz, mukesh27, SergeyBiryukov.
Fixes#33058.
Built from https://develop.svn.wordpress.org/trunk@55556
git-svn-id: http://core.svn.wordpress.org/trunk@55068 1a063a9b-81f0-0310-95a4-ce76da25c4cd