The ornamental design for a sidingcornercover, as shown and described.
FIG. 1 is a perspective view of a siding corner cover showing my new design in a position of use;
FIG. 2 is a front right side view of the siding corner cover;
FIG. 3 is a front left side view of the siding corner cover;
FIG. 4 is a rear right side view of the siding corner cover;
FIG. 5 is a rear left side view of the siding corner cover;
FIG. 6 is a top view of the siding corner cover; and,
FIG. 7 is a bottom view of the siding corner cover.
The circular features on the cover itself depict portions of the siding corner cover that form no part of the claimed design. The remaining broken lines in FIG. 1 depict environmental subject matter that forms no part of the claimed design.