The ornamental design for a chair, as shown and described.
FIG. 1 is a front elevational view of a chair showing my design;
FIG. 2 is a rear elevational view of the chair:
FIG. 3 is a top plan view of the chair;
FIG. 4 is a bottom plan view of the chair;
FIG. 5 is a right side elevational view of the chair; the left side elevational view being a mirror image thereof; and,
FIG. 6 is a cross-sectional view of the chair cut along section line 6-6 shown in FIG. 1.
Throughout the views, the evenly spaced broken lines illustrate the portions of the chair that form no part of the claimed design. The dot-dashed broken lines represent the boundaries of the design and form no part of the claim. The thin, parallel lines represent surface shading and not ornamentation or decoration.