The ornamental design for a slidingdoorstop, as shown and described.
FIG. 1 is an exploded perspective view of a door stop showing my new design in use;
FIG. 2 is an assembled side elevation thereof viewed perpendicular to a sliding door track, the opposite side being a mirror image;
FIG. 3 is an assembly side elevation thereof viewed in line with the sliding door track, the opposite side being a mirror image;
FIG. 4 is a top view thereof; and,
FIG. 5 is a bottom view thereof.
The floor and sliding doors shown in broken lines in FIG. 1 denote the nature and environmental use of the design and are not part of the claimed design.