The ornamental design for a concealed bottleholder, as shown and described.
FIG. 1 is a top perspective view of the concealed bottle holder showing my new design;
FIG. 2 is a side elevation view thereof;
FIG. 3 is another side elevation view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof; and,
FIG. 6 is a perspective view of the concealed bottle holder shown in use, with the broken line showing of environment being for illustrative purposes only and forming no part of the claimed design.