The ornamental design for a controlbox, as shown and described.
FIG. 1 is a bottom plan view of a control box showing my design;
FIG. 2 is a front elevation view of the control box;
FIG. 3 is a perspective view of the control box;
FIG. 4 is a left side elevation view of the control box;
FIG. 5 is a right side elevation view of the control box; and,
FIG. 6 is a top plan view of the control box.
Throughout the Figures, the broken lines are included for the purpose of illustrating the environment of the design and form no part of the claimed design.