We claim the ornamental design for a handheld electronic device, as shown and described.
FIG. 1 is a front perspective view of a handheld electronic device;
FIG. 2 is a front elevational view of the handheld electronic device;
FIG. 3 is a left elevational view thereof;
FIG. 4 is a right elevational view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan 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.