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 left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines depicting portions of the body of the handbag, the chain with handle, zipper, zipper pull, and bottom feet show unclaimed subject matter for the design.