We claim the ornamental design for a handheld electronic device, as shown and described.
FIG. 1 is a back perspective view of a handheld electronic device showing the new design.
FIG. 2 is a back elevational view of the handheld electronic device;
FIG. 3 is a left elevational view thereof; and,
FIG. 4 is a right elevational view thereof.
The broken lines shown in the drawings are for the purpose of illustrating unclaimed portions of the handheld electronic device and form no part of the claimed design.