We claim the ornamental design for a portable computer, as shown and described.
FIG. 1 is a rear perspective view of a portable computer of the present invention;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a first side view thereof;
FIG. 5 is a second side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines in the drawings represent portions of the portable computer that form no part of the claimed design. Additionally, the dash-dot-dashed lines in the drawings define the boundaries of the claimed design.