The ornamental design for a supportstand, as shown and described.
FIG. 1 is a front perspective view of a support stand in which the rear perspective is identical to FIG. 1 of a first embodiment showing my new design;
FIG. 2 is a front perspective view in which the rear perspective view is identical to FIG. 2 of a second embodiment; and,
FIG. 3 is a side view of the first and second embodiments as shown in FIGS. 1 and 2.
The design has a bottom that is unornamented and therefore is omitted from the drawing. The broken lines shown in FIG. 2 represent unclaimed environmental structure and are shown for illustrative purposes only and form no part of the claimed design.