The ornamental design for a flowerbox, as shown and described.
FIG. 1 is a front isometric view of a flower box in accordance with the new design;
FIG. 2 is a top view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a rear view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines depict features of the flower box that form no part of the claim. Broken lines and the areas within them in FIG. 2 depict portions of the flower box that from no part of the claimed design.