The ornamental design for a handbag, as shown and described.
1. Handbag
1.1 : Perspective
1.2 : Front
1.3 : Back
1.4 : Left
1.5 : Right
1.6 : Top
1.7 : Bottom
The broken lines in the figures are for the purpose of illustrating claimed stitching; 1.1 is a perspective view of a handbag; 1.2 is a front view thereof; 1.3 is a back view thereof; 1.4 is a left side view thereof; 1.5 is a right side view thereof; 1.6 is a top view thereof;. 1.7 is a bottom view thereof.