The ornamental design for a chair, as shown and described.
FIG. 1 is a front perspective view of a chair showing our new design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof;
FIG. 7 is a right side view thereof;
FIG. 8 is a left side view thereof; and,
FIG. 9 is an enlarged sectional view thereof taken along section line A—A in FIG. 3, in which a portion of the chair is not shown in order to provide the enlarged view.