The ornamental design for a serverunit with door, as shown and described.
FIG. 1 is a front view of a server unit with door showing our design;
FIG. 2 is a front view thereof without the door;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof; and,
FIG. 5 is a side view thereof.
The broken lines in the drawings illustrate portions of the server unit, or door, or environment and form no part of the claimed design. Cross-hatched lines in the drawings illustrate color and form no part of the claimed design.