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 thereof;
FIG. 3 is a right elevational view thereof;
FIG. 4 is a left 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 of the handheld electronic device are for the purpose of illustrating portions of the article and form no part of the claimed design.