The ornamental design for a diaper accessory, as shown and described.
FIG. 1 is a front perspective view of a diaper accessory in accordance with the 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;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a front view of the diaper accessory shown in an alternate position of use with the front flap overlain atop a diaper.
The broken lines shown in FIGS. 1-7 represent the bounds of the claim and form no part of the claimed design. The additional broken lines shown in FIG. 8 illustrate environment and form no part of the claimed design.