The ornamental design for a chair, as shown and described.
FIG. 1 is a front view thereof;
FIG. 2 is a back view thereof;
FIG. 3 is a left side view thereof,
FIG. 4 is a right view thereof;
FIG. 5 is top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is the perspective view of the chair showing my new design.
The broken lines in the figures shown structure or boundaries for illustrative purpose only and are not part of the claimed design, but rather show portions of the article in which the design is embodied or applied to that are not considered part of the claimed design. The broken lines shall form no part of the claimed design.