The ornamental design for a handbag, as shown and described.
FIG. 1 is a front 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 left side view thereof;
FIG. 5 is right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is an environmental, front perspective view of the handbag shown in FIG. 1.
The small broken lines on the handbag represents stitching and forms part of the claimed design. The broken lines showing a shoulder strap are for the purposes of illustrating environment and form no part of the claimed design.