I claim the ornamental design for a diaper bag, as shown and described.
FIG. 1 is a Perspective view of a diaper bag showing my new design;
FIG. 2 is a Front view of the diaper bag as shown in FIG. 1;
FIG. 3 is a Back view of the diaper bag as shown in FIG. 1;
FIG. 4 is a Right-side view of the diaper bag as shown in FIG. 1;
FIG. 5 is a Left-side view of the diaper bag as shown in FIG. 1;
FIG. 6 is a Top view of the diaper bag as shown in FIG. 1; and,
FIG. 7 is a Bottom view of the diaper bag as shown in FIG. 1.
The broken lines illustrating zipper pulls form no part of the claimed design. The remaining broken lines illustrate stitching that forms part of the claimed design.