The ornamental design for a handbag, as shown and described.
FIG. 1 is a front perspective view of the handbag 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, metal portions, and side rivets show unclaimed subject matter for the design.