Fix the output if there are no image tags.

Boy, that was dumb - "0/6" could mean no images out of 6 tags, or no image
tags, but 6 other images.  Now it's "0" if there really are no images;
"0/6" for the former case; and simply "6" for the latter; it's still
"0/6/12" if there are no images out of 6 tags, with 12 images in total.