The ornamental design for a chair, as shown and described.
FIG. 1 is a front perspective view of a chair embodying my new design;
FIG. 2 is a rear perspective view of the chair;
FIG. 3 is a front elevational view of the chair;
FIG. 4 is a side elevational view of one side of the chair, the two sides being mirror images of one another;
FIG. 5 is a rear elevational view of the chair; and,
FIG. 6 is a top plan view of the chair.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design, while all other broken lines are directed to environment and are for illustrative purposes only; the broken lines form no part of the claimed design.