The ornamental design for an article holder, as shown and described.
FIG. 1 is an upper, front, left side perspective view of an article holder, showing my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a front elevational view thereof, the back elevation being a mirror image thereof; the environment comprising a taco shell is shown in dashed lines for illustrative purposes only; and,
FIG. 5 is a right side elevational view thereof, the left side elevation being a mirror image thereof; the environment comprising a taco shell is shown in dashed lines for illustrative purposes only.