The ornamental design for a chair, as shown and described.
FIG. 1 is a front perspective view of an embodiment of a chair showing my 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; and,
FIG. 6 is a top view thereof.
The dashed lines shown in FIGS. 1-6 are included for the purpose of illustrating environmental subject matter only and form no part of the claimed design. In the embodiment shown in FIGS. 1-6, the material that covers the seat back and bottom is comprised of a wire mesh material. The bottom view is omitted and forms no part of the claimed design.