The ornamental design for a handpillow, as shown and described.
FIG. 1 is a top front perspective view of a first exemplary embodiment of a hand pillow, showing my design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a side view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The dashed broken lines shown in the drawings are for the purpose of illustrating unclaimed portions of the hand pillow, and forms no part of the claim.