The code used to fall back to anonymous login independently for username
and password; however, it should only use a fall-back password if the
username is missing or (case-insensitive) "anonymous". When a
non-anonymous username is given without password, we should simply skip
he PASS message to FTP.
If the FTP server requests a password, in the latter case, QFtp will
signal authenticationRequired; in all cases, if the server rejects the
given credentials, QFtp signals authenticationFailed. Either way, the
client code can then query the user for credentials as usual.
Task-number: QTBUG-25033
Change-Id: I2a4a3b2725819ab19c8a7e4baa431af539edcd8d
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
a5ad605dfe