The ornamental design for a wristwatch, as shown and described.
The file of this patent contains a drawing/photograph executed in color. Copies of this patent with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
The FIGURE is a top view of a wristwatch of the present design. The wristwatch is flat, the undisclosed sides, top, bottom, and rear views are not part of the claimed design.