The ornamental design for an tabletholder, as substantially shown and described.
FIG. 1 is a front, left perspective view of a tablet holder my new design;
FIG. 2 is a front elevation view of FIG. 1;
FIG. 3 is a rear elevation view of FIG. 1;
FIG. 4 is a left side elevation view of FIG. 1;
FIG. 5 is a right side elevation view of FIG. 1;
FIG. 6 is a top plan view of FIG. 1;
FIG. 7 is a bottom plan view of FIG. 1; and,
FIG. 8 is an exploded perspective view of FIG. 1.
The broken lines showing the tablet in FIGS. 1-3, 6, and 8-10 are included for the purpose of showing an article that forms no part of the claimed design.