I claim the ornamental design for a star configuration chair base, as shown and described.
FIG. 1 is a perspective view of a star configuration chair base according to my new design;
FIG. 2 is a reduced top plan view of the star configuration chair base of FIG. 1;
FIG. 3 is a reduced bottom plan view of the star configuration chair base of FIG. 1.
FIG. 4 is a reduced view in side elevation of the star configuration base of FIG. 1, the opposite side being a mirror image thereof; and,
FIG. 5 is a reduced perspective view of the star configuration chair base of FIG. 1, the broken lines of parts and parts other than the star configuration chair base being for illustrative purposes only and forming no part of my design.