The ornamental design for a wristwatch, as shown and described.
FIG. 1 is a top plan view of a wristwatch showing my new design, the watch strap being indicated only diagrammatically, its appearance not being claimed;
FIG. 2 is a bottom plan view thereof;
FIG. 3 is a side elevational view thereof;
FIG. 4 is a side elevational view thereof from the side opposite that shown in FIG. 3;
FIG. 5 is a view thereof from the top of FIG. 1;
FIG. 6 is a view thereof from the bottom of FIG. 1; and,
FIG. 7 is a top and side perspective view thereof.
The broken lines showing the strap are for illustrative purposes only and form no part of the claimed design.