The ornamental design for a soapholder, as shown and described.
FIG. 1 is a perspective view of our new design;
FIG. 2 is a side elevational view thereof, the other side being a mirror image;
FIG. 3 is a top plan view thereof; and,
FIG. 4 is front elevational view thereof.
The broken-line disclosure is understood to represent a portion of the article in which the claimed design is embodied, but which forms no part of the claimed design.