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 back elevational view thereof;
FIG. 4 is a right elevational view thereof;
FIG. 5 is a left elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The portions of the handheld electronic device shown in broken lines form no part of the claimed design. The boundary formed by the broken lines on the top surface of the handheld electronic device and unshaded area within form no part of the claimed design.