The ornamental design for a chair, as shown and described.
FIG. 1 is a front view of a chair embodying the design;
FIG. 2 is a left side view of the chair of FIG. 1, with a right side being a mirror image thereof;
FIG. 3 is a back view of the chair of FIG. 1;
FIG. 4 is a top view of the chair of FIG. 1;
FIG. 5 is a is a front perspective view of the chair of FIG. 1;
FIG. 6 is a back perspective view of the chair of FIG. 1; and,
FIG. 7 is a bottom perspective view of the chair of FIG. 1.
The broken lines shown in the figures are for illustrative purposes only and form no part of the claimed design. For example, the chair base is shown in broken lines and forms no part of the claimed design.