The ornamental design for a butterdish, as shown and described.
FIG. 1 is a top isometric view of a butter dish showing the new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is an end elevation view thereof;
FIG. 4 is a side elevation view thereof;
FIG. 5 is a bottom isometric view thereof; and,
FIG. 6 is a bottom plan view thereof.
The dashed lines shown in the drawings illustrate portions of the butter dish that form no part of the claimed design. The butter dish has longitudinal and lateral symmetry, with opposed sides being mirror images of each other.