The ornamental design for a sandal, as shown and described.
FIG. 1 is a perspective view of a sandal;
FIG. 2 is a front view of a sandal;
FIG. 3 is a rear view of a sandal;
FIG. 4 is a right-side view of a sandal;
FIG. 5 is a left-side view of a sandal;
FIG. 6 is a top view of a sandal; and,
FIG. 7 is a bottom view of a sandal.
The even spaced broken lines are unclaimed environment and form no part of the claimed design. Further, the dash dot dash lines immediately adjacent the solid-line portions of the design form the boundary of the design, forming no part of the claimed design.