The ornamental design for a chair, as shown and described.
FIG. 1 shows a front view of a first embodiment of a chair according to the present invention.
FIG. 2 shows a right side elevation view of the chair of FIG. 1, the left side elevation view being a mirror image of the right side elevation view.
FIG. 3 shows a top view of the chair of FIG. 1.
FIG. 4 shows a front view of a second embodiment of a chair according to the present invention.
FIG. 5 shows a right side elevation view of the chair of FIG. 4, the left side elevation view being a mirror image of the right side elevation view; and,
FIG. 6 shows a top view of the chair of FIG. 4.
Portions or features of the chair not shown in the drawings form no part of the claimed design.