The ornamental design for a slingbag, as shown and described.
FIG. 1 is a perspective view of a sling bag showing my new design with the zipper open;
FIG. 2 is a front view thereof with the zipper open;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof with the zipper open;
FIG. 5 is a rear view thereof with the zipper open;
FIG. 6 is a rear view thereof with the zipper closed;
FIG. 7 is a bottom view thereof with the zipper open; and,
FIG. 8 is a bottom view thereof with the zipper closed.
The broken lines showing straps and zippers are included for the purpose of illustrating the embodiment of the invention as it would be in use, and form no part of the claimed design.