Oh hey, I was walking dog and realized making wall lines longer wasn't going to work.
So you already figured to make wall erasers shorter good! But that still leaves us with the dots when walls erased all the way around.
There is a way to make a dot eraser: check every place walls intersect and use point() 1 pixel above&below, 1 pixel left&right of those places, if they are all white then make the center location white.