The ornamental design for a chair, as shown and described.
FIG. 1 is a perspective view 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;
FIG. 6 is a top view thereof; and,
FIG. 7 is another perspective view thereof with a seat cushion placed thereon.
The dot-dash broken line defines the boundary of the claimed design, which extends to the boundary but does not include the boundary, all other broken lines in the drawings are directed to environment. The broken lines form no part of the claimed design.