I claim the ornamental design for a chair, as shown and described.
FIG. 1 is a front view of a chair of the claimed design;
FIG. 2 is a rear view of the chair shown in FIG. 1;
FIG. 3 is a left side view of the chair shown in FIG. 1;
FIG. 4 is a top view of the chair shown in FIG. 1;
FIG. 5 is a magnified, bottom perspective view of the chair shown in FIG. 1; and,
FIG. 6 is a front perspective view of the chair shown in FIG. 1.
The ornamental design which is claimed is shown in the figures. Any colors and surface textures shown in the figures are not part of the claimed design.