[css-lists][css-counter-styles] Spacing after image bullet

Hi,

The CSSWG has decided that the spacing between marker and content should
depends on only the suffix of the counter style. However, it is not defined
what should happen for image bullets specified by list-styie-image. I
suggest that we should treat it as if the bullets have a default one space
suffix like graphic predefined bullets, but I'm not sure which spec this
problem belongs to.

- Xidorn