We claim the ornamental design for a holder for a portable computer, as shown and described.
FIG. 1 is a front perspective view of a holder for a portable computer of the present invention;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a first side view thereof;
FIG. 6 is a second side view thereof;
FIG. 7 is a top view thereof;
FIG. 8 is a bottom view thereof;
FIG. 9 is an end view taken along the line 9-9 in FIG. 3;
FIG. 10 is a rear perspective view thereof with the support pillars folded;
FIG. 11 is a rear perspective view of the holder thereof attached to a portable computer; and,
FIG. 12 is a rear perspective view thereof shown in an alternate environment.
The broken line showing of holder for a portable computer is included for the purpose of illustrating environment and forms no part of the claimed design.