The ornamental design of a handbag, as shown and described.
FIG. 1 is a perspective view thereof.
FIG. 2 is a front view thereof.
FIG. 3 is a rear 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 showing a hinge and an ornamental element on the fastening flap are for the purposes of illustrating environment and form no part of the claimed design.