The ornamental design for a headpiece, as shown and described.
FIG. 1 is a perspective view of a headpiece showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a right view thereof;
FIG. 5 is a left view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines showing a top portion seam and a strap portion seam are for the purpose of illustrating environmental structure and form no part of the claimed design.
The cross-hatched pattern, although shown intermittently, is meant to represent fabric, and is understood to be distributed uniformly over the surfaces of the claimed design.