Headphone case

FIG. 1 is a perspective view of an ornamental design for a headphone case;

FIG. 2 is a top view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a first side view thereof;

FIG. 5 is a second side view thereof;

FIG. 6 is a front view thereof; and,

FIG. 7 is a rear view thereof.

The broken lines in FIG. 3 illustrate an aspect of the case that forms no part of the claimed design.