The ornamental design for a headlamp, as shown and described.
FIG. 1 is a perspective view of a head lamp showing our new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The oblique line shading shown in the drawings indicates a transparent or translucent surface. Internal structure of the transparent or translucent surface is omitted. No claim is made to any elements inside the transparent or translucent surface. The broken lines showing portions of the head lamp represent unclaimed portions of the claimed design and form no part of the claimed design.