The ornamental design for a bottlestopper, as shown and described.
FIG. 1 is a front, top, and right side perspective view of a bottle stopper showing our new design in a position of use with an exemplary bottle;
FIG. 2 is a front, top, and right side perspective view thereof, shown with the exemplary bottle removed to show aspects of the design not visible when combined;
FIG. 3 is a rear, bottom, and left side perspective thereof;
FIG. 4 is front elevation thereof;
FIG. 5 is a right side elevation thereof;
FIG. 6 is a rear elevation thereof;
FIG. 7 is a left side elevation thereof;
FIG. 8 is a top plan view thereof; and,
FIG. 9 is a bottom plan view thereof.
The features shown in broken lines depict environmental subject matter only and form no part of the claimed design.