The ornamental design for clasp for handbag, as shown and described.
FIG. 1. is a front perspective view of a clasp for handbag showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a back view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The short dotted lines illustrate portions of the handbag and form no part of the claimed design. Portions of the clasp not visible in the Figures form no part of the claim.