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 flap attached to the rear wall is extended upward and to the rear; 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.