The ornamental design for a cornermember for casing, as shown and described.
FIG. 1 is a perspective view of a corner member for casing showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a left side elevational view thereof; and
FIG. 7 is a right side elevational view thereof; and,
FIG. 8 is an isometric view of the corner member for casing shown in condition of use.
The broken line showing of environmental structure and additional corner members for casing is for illustrative purposes only and forms no part of the claimed design.