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 back perspective view of the handheld electronic device;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a back elevational view thereof;
FIG. 5 is a right elevational view thereof;
FIG. 6 is a left elevational view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken lines adjacent to the shade lines define the boundary of the design. Other broken lines illustrate the disclaimed portions of the design. None of the broken lines form part of the claimed design.