The ornamental design for a case for a handheld electronic device, as shown and described.
FIG. 1 is a perspective view of a case.
FIG. 2 is a front view of the case of FIG. 1.
FIG. 3 is a rear view of the case of FIG. 1.
FIG. 4 is a right side view of the case of FIG. 1.
FIG. 5 is a left side view of the case of FIG. 1.
FIG. 6 is a top view of the case of FIG. 1; and,
FIG. 7 is a bottom view of the case of FIG. 1.
The dot-dot broken lines show unclaimed subject matter, and form no part of the claimed design. The dot-dash broken lines are included to show the boundary of the claimed design and likewise form no part of the claimed design.