[PATCH] Assume "unknown" terminal type by default

[Eli Zaretskii]

> From: Stephanos Ioannidis <root@stephanos.io>
> Date: Tue,  2 Jun 2020 12:52:49 +0900
> Cc: Stephanos Ioannidis <root@stephanos.io>
> 
> This patch modifies the `_rl_init_terminal_io` function to pass
> `unknown` terminal type instead of `dumb` when no terminal name is
> provided by the caller (e.g. when the `TERM` environment variable is
> not set on Win32).
> 
> This ensures that the termcap provider (e.g. ncurses) resolves the
> default preferred terminal type instead of using the `dumb` terminal
> type.

Isn't this something that ncurses itself should do on MS-Windows?