The ornamental design for a handbag, as shown and described.
FIG. 1 is a perspective view of a handbag showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The dash-dash broken lines illustrate portions of the handbag and form no part of the claim. The dash-dot-dash broken lines encircling the interior of the bag depict the claim boundary. The interior of the bag inside the claim boundary forms no part of the claim.