Add error reporting to get_console_input_win32().

Add error reporting to get_console_input_win32().

When the function setup fails due to invalid file handles, or because
WriteFile(err, ...) fails (due to file handle corruption elsewhere),
the function used to silently "return false"

Change this to print a M_WARN|M_ERRNO message.

Also, change the function style to early-return style (= large diff, but
most are indent changes only).

v2: fix spurious "}" that was left over from change to early-return.

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Message-Id: <20210618181246.30769-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22577.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>