The ornamental design for a handbag, as shown and described.
FIG. 1 is a front elevational view of the handbag of the present invention;
FIG. 2 is a back elevational view thereof;
FIG. 3 is a left side elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a perspective view thereof.
The broken line showing of a portion of the handbag and shoulder straps are for the purposes of illustrating environment and form no part of the claimed design.