The ornamental design for a handbag, as shown and described.
FIG. 1 is a ¾ perspective view thereof;
FIG. 2 is front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is an open perspective view thereof.
The broken lines shown in the figures are included for the purpose of illustrating the environment in which the design is used and form no part of the claimed design.