yopts: Return SPECIAL on stop-scan choice

Signed-off-by: Pavel Emelyanov <xemul@sacred.ru>
yopts: Check for arguments being assigned at the end of parsing

Check the number-of-args variable, not the if (!arg_var), because
for int args zero can be valid value.

Signed-off-by: Pavel Emelyanov <xemul@sacred.ru>