The ornamental design for a handbag, as shown and described.
FIG. 1 is a front perspective view of a handbag showing my handbag design;
FIG. 2 is a front view of the handbag thereof;
FIG. 3 is a rear view of the handbag thereof;
FIG. 4 is a right side view of the handbag thereof;
FIG. 5 is a left side view of the handbag thereof;
FIG. 6 is a top view of the handbag thereof; and,
FIG. 7 is a bottom view of the handbag thereof.
The broken line showing of the handles, portion of the closure flap, grommets, studs, portion of the rope, and portions of the bag structure is for illustrative purposes only and forms no part of the claimed design.