The ornamental design for a chair, as shown and described.
FIG. 1 is a front view of a chair bearing the design;
FIG. 2 is a rear view thereof
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a front-left perspective view thereof.
The broken lines showing portions of the chair form no part of the claimed design.
The gray shading shown on the chair surface in the drawings represents a contrast in appearance between portions of the chair surface and chair legs, and forms no part of the claimed design.