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 that extends from the left side to the right side being draped around the front and left 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 without the shoulder strap, where the top center zipper is unzipped, 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 that forms part of the claimed design.