[tin 1.7.x] endless authentication loop

if the username given in ~/.newsauth is wrong tin ends up in an
endless authentication loop as you can not correct the username at
the prompt anymore:

| Authorization failed for user: wrong
| Server expects authentication.
|   Please enter username: wrong

^U and/or ^? to delete the wrong username and type in the correct one
lead to:

|   Please enter username: right
|   Please enter password: password
! Authorization failed for user: wrong
| Server expects authentication.

and now we are in a loop without any way to exit it.

anyone willing to look at this? (p.s.: seen on Linux/ncusesw-5.4)

urs
-- 
"Only whimps use tape backup: _real_ men just upload their important stuff
 on ftp, and let the rest of the world mirror it ;)" - Linus