The ornamental design for a chair, as shown and described.
FIG. 1 is a perspective view of a chair embodying the new design and including a backrest, a seat, a frame, and a fastening assembly including a first fastener and a second fastener.
FIG. 2 is a front view thereof.
FIG. 3 is a rear view thereof.
FIG. 4 is a first side view thereof.
FIG. 5 is a second side view thereof; and,
FIG. 6 is a top view thereof.
All features in broken lines are for the purpose of illustrating environmental structure and form no part of the claimed subject matter.