gladevcp -pass on the fact there was an error

If there was an error and you ask for the value send None instead of 0
Also if 'Error' is on screen the next key press should clear the error.
hey now it does!
gscreen -fix numeric input errors defaulting to zero

If there was an error it returned as 0 so for instance
on tool index it would index to tool zero. now it just
doesn't accept it, you must cancel or fix it.