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, having a shoulder strap being draped across the front side and connecting at the left 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 bottom plan view thereof; and,
FIG. 8 is a front left perspective view of the handbag in an alternate configuration, in which the upper triangular flap on the front face has been rotated over the top side toward the rear side.
The broken lines depict stitching and are included in the claimed design.