The ornamental design for a cardholder, as shown and described.
FIG. 1 is a perspective view of a card holder, illustrating my new design;
FIG. 2 is a top plan view of the card holder;
FIG. 3 is a bottom plan view of the card holder;
FIG. 4 is a front elevational view of the card holder;
FIG. 5 is a rear elevational view of the card holder;
FIG. 6 is a right side elevational view of the card holder;
FIG. 7 is a left side elevational view of the card holder; and,
FIG. 8 is a perspective view of the card holder, illustrating the manner in which it is used.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design, while all other broken lines are shown for the purpose of illustrating environment only; the broken lines form no part of the claimed design.