We claim the ornamental design for a bottle stopper, as shown and described.
FIG. 1 is a top plan view of the bottle stopper according to the present design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a right side elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a left side elevational view thereof;
FIG. 7 is an exploded front top perspective view of the bottle stopper shown with the O-rings removed and relocated below the bottle stopper for clarity of disclosure;
FIG. 8 is a front top perspective view thereof;
FIG. 9 is a front bottom perspective view thereof;
FIG. 10 is a front top perspective view of the bottle stopper of FIG. 1 shown in a position of use with a first means of attachment for a decorative element drawn in broken lines; and,
FIG. 11 is a front top perspective view of the bottle stopper of FIG. 1 shown in a position of use with a second means of attachment for a decorative element drawn in broken lines.
The broken lines showing the means of attachment for a decorative element in FIGS. 10 and 11 depict environment and form no part of the claimed design.