An ornamentaldesign of a chair, as shown and described.
FIG. 1 is a perspective view of our new design for a chair;
FIG. 2 is a front view thereof;
FIG. 3 is a right view thereof;
FIG. 4 is a back view thereof;
FIG. 5 is a left view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
Various figures are illustrated with various grayscale levels of surface shading to show various contrasting appearances of different portions of this design. No particular color or design pattern is claimed.