In FTP Transport, checking if a resource is a file degrades performance

This is caused because the FTPClient API doesn't provide a direct way to check if a path belongs to a file or a directory.

The current implementation lists all the files from the given path, and check if the list only has an element and if this element is a file. However, this is very expensive if you list a  directory with thousands of files. 

A best approach could be list only the first file of the given patch.