avformat/ftp: Support response code 125 for STOR and RETR commands

This fixes a problem where ffmpeg would hang if there is already an open
data connection, and the server sends a 125 response code in reply to a
STOR or RETR command.

Signed-off-by: Raymond Hilseth <rhi@vizrt.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>