qga-win32: Improve guest-set-user-password, guest-file-open errors

When guest-set-user-password's argument @password can't be converted
from UTF-8 to UTF-16, we report something like

    Guest agent command failed, error was 'Invalid sequence in conversion input'

Improve this to

    can't convert 'password' to UTF-16: Invalid sequence in conversion input

Likewise for argument @username, and guest-file-open argument @path,
even though I'm not sure you can actually get invalid input past the
QMP core there.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240514105829.729342-2-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Konstantin Kostiuk <kkostiuk@redhat.com>
1 file changed