The ornamental design for a shelfunit, as shown and described.
FIG. 1 is a front perspective view of a shelf unit showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines shown in the drawings represent portions of the shelf unit that form no part of the claimed design. The dot-dashed lines in the figures represent boundary lines defining a boundary of certain aspects of the claimed design.