The ornamental design for a portion of a sandal, as shown and described.
FIG. 1 is a front perspective view of a portion of a sandal showing my new design;
FIG. 2 is a left side view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a back view thereof; and,
FIG. 6 is a top view thereof.
The broken line showing of the sole, buckles, straps, portion of the front, portion of the upper, and buckle holes is for illustrative purposes only and forms no part of the claimed design.