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 view thereof, the left side being a mirror image thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a top view thereof; and,
FIG. 6 is a bottom view thereof.
The broken lines in the drawings illustrate a symbolic break in the length of the chair. The appearance of any portion of the chair between the break lines forms no part of the claimed design.