The ornamental design for a handbag, as shown and described.
FIG. 1 is a perspective view of the handbag of the present invention.
FIG. 2 is a front elevation view of the handbag.
FIG. 3 is a rear elevation view of the handbag.
FIG. 4 is a left side elevation view of the handbag.
FIG. 5 is a right side elevation view of the handbag.
FIG. 6 is a plan view of the handbag; and,
FIG. 7 is a bottom view of the handbag.
The broken line showing of a handle and a portion of a handbag is included for the purpose of illustrating environment and forms no part of the claimed design.