Fix incorrect cast when parsing FTP connection port

[kimci86]

Description

This commit fixes a regression introduced in eb19331 as part of PR #1846.

How to test this PR?

• Start a local FTP server. I used pyftpdlib.

  pip3 install --user pyftpdlib
  python3 -m pyftpdlib -u user -P pass

• Edit SFML's example program ftp to use port 2121 (pyftpdlib's default port).
  Note I am not using port 21 to avoid having to run the server as root.

  diff --git a/examples/ftp/Ftp.cpp b/examples/ftp/Ftp.cpp
  index e4de8adc..469937a9 100644
  --- a/examples/ftp/Ftp.cpp
  +++ b/examples/ftp/Ftp.cpp
  @@ -36,7 +36,7 @@ int main()
  
       // Connect to the server
       sf::Ftp server;
  -    sf::Ftp::Response connectResponse = server.connect(address);
  +    sf::Ftp::Response connectResponse = server.connect(address, 2121);
       std::cout << connectResponse << std::endl;
       if (!connectResponse.isOk())
           return EXIT_FAILURE;

• Compile and run SFML's example program ftp.

Without the patch, the example program cannot gather the content of the server's working directory.
With the patch, it can :)

[vittorioromeo]

Nice catch! We should have tests for this stuff... :)