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 of the handbag shown in FIG. 1;
FIG. 3 is a back view of the handbag shown in FIG. 1;
FIG. 4 is a left side view of the handbag shown in FIG. 1 (with the right side view being a mirror image thereof);
FIG. 5 is a top view of the handbag shown in FIG. 1; and,
FIG. 6 is a bottom view of the handbag shown in FIG. 1.
The broken lines showing the handle, buckles and buckle rings are for the purposes of illustrating environment and forms no part of the claimed design.