We claim the ornamental design for a chair, as shown and described.
FIG. 1 is front view of a chair;
FIG. 2 is rear view of the chair;
FIG. 3 is a side view of the chair;
FIG. 4 is a top view of the chair;
FIG. 5 is a bottom view of the chair; and,
FIG. 6 is a perspective view of the chair.
Applicant notes that the side view of the chair as shown in FIG. 3 is representative of both a right side view and left side view of the chair. Any subject matter shown in dashed lines, and any surfaces of the design not shown, including interior surfaces, form no part of the claimed invention.