The ornamental design for a wristwatch, as shown and described.
FIG. 1 is a perspective view of the front and right side of a wristwatch showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is perspective view of the rear and right side thereof.
The structural features depicted by broken lines in the drawings have been shown for the purpose of illustrating portions of the wrist watch that form no part of the claimed design.