The ornamental design for a chair, as shown and described.
FIG. 1 is a front perspective view of the chair embodying the new design;
FIG. 2 is a right side elevation view thereof, the left side being a mirror image thereof;
FIG. 3 is a front elevation view thereof;
FIG. 4 is a rear elevation view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
FIGS. 1-4 and 6 show portions of a chair in broken lines. The portions shown in broken lines are for environmental purposes only and form no part of the claimed design. The chair is shown with a symbolic break in its width. The appearance of any portion of the article between the break lines forms no part of the claimed design.