The ornamental design for a cooler, as shown and described.
FIG. 1 is a perspective view of a cooler with an open lid that has an upper surface that includes a wood layer.
FIG. 2 is a right side view of the cooler of FIG. 1.
FIG. 3 is a left side view of the cooler of FIG. 1.
FIG. 4 is a top view of the cooler of FIG. 1.
FIG. 5 is a bottom view of the cooler of FIG. 1
FIG. 6 is a front view of the cooler of FIG. 1; and,
FIG. 7 is a rear view of the cooler of FIG. 1.
The broken lines in the figures illustrate the environment of the claimed design and form no part of the claimed design. The boundary lines in the drawings indicate that any portion of the article beyond what is shown forms no part of the claimed design.