The ornamental design for a sandal, as shown and described.
FIG. 1 is a right elevation view of a sandal showing our new design;
FIG. 2 is a left elevation view thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is an isometric view thereof; and,
FIG. 8 is a perspective view of another embodiment thereof without beads, all other views being substantially the same as FIGS. 1-6, the only difference being the removal of the beads.