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
1.8 : Reference view
The broken lines in the figures are for the purpose of illustrating claimed stitching; 1. is a perspective view of a handbag; 2. is a front view thereof; 3. is a back view thereof; 4. is a left side view thereof; 5. is a right side view thereof; 6. is a top view thereof; 7. is a bottom view thereof; 8. is a reference view thereof; The reference view shown in reproductions 1.8 forms no part of the design.