The ornamental design for a handbag, as shown and described.
FIG. 1 is a front perspective view of a handbag showing my new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side view thereof, the right side view being a mirror image thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a top plan view in an alternate configuration, where the front and rear walls of the handbag are spread apart, and the top side snaps are undone; and,
FIG. 7 is a bottom view of the configuration shown in FIG. 5.
The broken lines depict stitching and are part of the claimed design.