curses: Disable echoing if backspace is pressed first.
* pinentry/pinentry-curses.c (struct dialog): New fields got_input, no_echo. (dialog_input): Disable echoing and display instead "[no echo]" if the backspace key is pressed first.
- GnuPG-bug-id: T3428
- Signed-off-by: Damien Goutte-Gattat <dgouttegattat@incenp.org>