The ornamental design for a windowblindcover, as shown and described.
FIG. 1 is a front view of the window blind cover.
FIG. 2 is a side view of the window blind cover.
FIG. 3 is a top view of the window blind cover.
FIG. 4 is a bottom view of the window blind cover; and,
FIG. 5 is a front view of the window blind cover in use. The broken lines depict unclaimed areas immediately adjacent to the claimed design and identify portions of the design that form no part of the claimed design.
The design is shown broken away to indicate that the window blind cover has no specific length.