I claim the ornamental design for a post connector, as shown and described.
FIG. 1 is a top right front perspective view of a post connector showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a right side view thereof, the left side view being a mirror image thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a bottom perspective view thereof; and,
FIG. 7 is a reduced top right front perspective view thereof shown in use condition, the two posts shown in broken lines form no part of the claimed design.