The ornamental design for a slingbag, as shown and described.
FIG. 1 is a front elevation view of the sling bag;
FIG. 2 is a rear elevation view of the sling bag;
FIG. 3 is a left side elevation view of the sling bag;
FIG. 4 is a right side elevation view of the sling bag;
FIG. 5 is a top view of the sling bag;
FIG. 6 is a bottom view of the sling bag;
FIG. 7 is a left side perspective view of the sling bag;
FIG. 8 is a right side perspective view of the sling bag;
FIG. 9 is a front perspective small interior view of the sling bag; and,
FIG. 10 is a front perspective large interior view of the sling bag.
The various components shown in broken line illustrations are shown in broken lines for illustrative purposes only and form no part of the claimed design.