The ornamental design for a chair, as shown and described.
FIG. 1 is a perspective view from the front side of a chair.
FIG. 2 is a perspective view from the rear side thereof.
FIG. 3 is a front elevation view thereof.
FIG. 4 is a rear elevation view thereof.
FIG. 5 is a right side elevation view thereof.
FIG. 6 is a left side elevation view thereof.
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
All of the material from the Japanese Design Application which is essential to the claimed design is included herein. Any material in the Japanese Design Application which is not present herein forms no part of the claimed design.