The ornamental design for a headlamp, as shown and described.
FIG. 1 is a perspective view of a head lamp showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is another perspective view thereof shown in an alternate configuration with the rear part rotated out.
The oblique line shading shown in the drawings indicates a transparent surface. The dashed broken lines illustrate portions of the article that form no part of the claimed design. The dot-dash broken lines represent the boundaries of the claimed design, and form no part thereof.