The ornamental design for a monitorunit, as shown and described.
FIG. 1 is a front view of a monitor unit showing our new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a left side view thereof, the right side view being a mirror image thereof;
FIG. 4 is a top view thereof; and,
FIG. 5 is a front perspective view thereof.
The broken lines in the Figures show portions of the monitor unit that form no part of the claimed design. The bottom view is omitted and forms no part of the claimed design.