The ornamental design for a knifebag, as shown and described.
FIG. 1 is a front view of a knife bag showing my new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a right side elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof;
FIG. 7 is a top view thereof, with the knife bag shown in an opened state with the inner panels closed;
FIG. 8 is a top view thereof, with the inner panels shown opened; and,
FIG. 9 is a bottom view thereof.
The broken lines depicting stitching form no part of the claimed design. All other broken lines depict portions of the knife bag that form no part of the claimed design.