The ornamental design for a chair, as shown and described.
FIG. 1 is a front perspective view of the chair.
FIG. 2 is a front view of the chair of FIG. 1.
FIG. 3 is a top view of the chair of FIG. 1.
FIG. 4 is a bottom view of the chair of FIG. 1.
FIG. 5 is a right view of the chair of FIG. 1.
FIG. 6 is a left view of the chair of FIG. 1; and,
FIG. 7 is a back view of the chair of FIG. 1.
The color of the chair forms no part of the claimed design. Shading shown on surfaces of the claim represents contour and does not represent any particular color, material, texture or finish.