The ornamental design for a tablebase, as shown and described.
FIG. 1 is a first perspective view of a table base;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a side view thereof, the opposing side being identical;
FIG. 4 is a front view thereof, the rear being identical;
FIG. 5 is a top view thereof; and,
FIG. 6 is a bottom view thereof.
The uniform broken lines shown in the drawings are included for purposes of illustrating portions of the table base that form no part of the claimed design; whereas, the non-uniform broken lines shown in the drawings are included for purposes of illustrating environment and form no part of the claimed design.