FIG. 1 is a front-left side perspective view of a chair showing our new design; FIG. 2 is a front perspective view thereof; FIG. 3 is a rear perspective view thereof; FIG. 4 is a left side perspective view thereof; FIG. 5 is a right side perspective view thereof; and, FIG. 6 is a top perspective view thereof. The unshown portions of the underside of the chair form no part of the claimed design.