The ornamental design for a cornershelf, as shown and described.
FIG. 1 is a top and front perspective view of a corner shelf showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a left side elevational view thereof; and,
FIG. 7 is a reduced top and front perspective view thereof, with the broken-line disclosure being for illustrative purposes only and forming no part of the claimed design.
The dash lines in FIGS. 1-7 are for illustrative purposes only showing environmental subject matter and form no part of the claimed designs.