The ornamental design for a chair, as shown and described.
FIG. 1 is a front perspective view of a chair.
FIG. 2 is a rear perspective view 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.
The broken lines shown in the drawings illustrate portions of the chair that form no part of the claimed design. The dot-dash lines show an unclaimed boundary which forms no part of the claimed design. The backrest sheet and the seat of the chair are made of mesh and the mesh pattern of the backrest sheet and the seat forms no part of the claimed design.