The ornamental design for a tablebase, as shown and described.
FIG. 1 is a perspective view of a table base of the present invention, illustrating a circular table top in phantom outline, the broken lines showing the table top for illustrative purposes only and forming no part of the claimed design;
FIG. 2 is a perspective view of the table base of the present invention, illustrating a square table top in phantom outline, the broken lines showing the table top for illustrative purposes only and forming no part of the claimed design;
FIG. 3 is a front elevational view of the invention, the rear elevational view being a mirror image thereof;
FIG. 4 is a right-side elevational view of the invention, the left-side elevational view being a mirror image thereof;