We claim the ornamental design for a cooler, as shown and described.
FIG. 1 is a top perspective view of a cooler showing our new design.
FIG. 2 is a bottom plan view thereof.
FIG. 3 is a front view thereof.
FIG. 4 is a rear view thereof.
FIG. 5 is a right side view thereof.
FIG. 6 is a left side view thereof.
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken dot-dash lines define boundaries of the claimed design and form no part thereof. The other broken lines in the drawings are for illustrative purposes only and form no part of the claimed design.