The ornamental design for a wristwatch, as shown and described.
FIG. 1 is a front perspective view of a wristwatch in accordance with the present design;
FIG. 2 is a front view of the wristwatch of FIG. 1;
FIG. 3 is a rear view of the wristwatch of FIG. 1;
FIG. 4 is a bottom view of the wristwatch of FIG. 1;
FIG. 5 is a right side view of the wristwatch of FIG. 1; and,
FIG. 6 is a left side view of the wristwatch of FIG. 1.
The broken lines on the wristwatch show portions of the wristwatch that form no part of the claimed design. The broken lines showing portions of a band illustrate environmental structures and form no part of the claimed design.