The ornamental design for a handbag, as shown and described.
FIG. 1 is a front left perspective view of a handbag showing my new design, with a shoulder strap being draped around the front and right sides;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a top plan view in an alternate configuration, where the front flap is rotated around the top side and toward the rear side, and the front and rear sides are spread open toward the front and rear, respectively; and,
FIG. 8 is a bottom view of the configuration shown in FIG. 6.
The broken lines depict stitching and are included in the claimed design.