We claim the ornamental design for a portable electronic device, as shown and described.
FIG. 1 is a front perspective view of a portable electronic device showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left-side view thereof;
FIG. 5 is a right-side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The short dash-dash broken line in the figures shows portions of the portable electronic device and the dot-dash broken line in the figures represents a boundary of the claimed design; the broken lines form no part of the claimed design.