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 elevation view thereof;
FIG. 3 is a back elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The evenly-dashed broken lines depict portions of the handbag that form no part of the claimed design. The dash-dot-dash broken lines depict the claim boundary and form no part of the claimed design. Any portion of the article shown inside the claim boundary forms no part of the claimed design.