The ornamental design for a tablebase, as shown and described.
FIG. 1 is a perspective view of a table base showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a right side elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a perspective view to more fully illustrate the table base without a table top.
The phantom lines in FIGS. 1-6 are for illustrative purposes only to show a sample table top and form no part of the claimed design. The bottom of the table base is not a part of the claimed design.