The ornamental design for a weightplate, as shown and described.
FIG. 1 is a perspective view of a weight plate showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a left side elevational view thereof; and,
FIG. 4 is a top plan view thereof.
The rear elevational view, the right side elevational view and the bottom plan view of the weight plate are respectively identical to the front elevational view, the side elevational view and the top plan view thereof.