I claim the ornamental design for a night light cover, as shown and described.
FIG. 1 is a perspective view of a night light cover, showing my new design;
FIG. 2 is a front elevational view thereof, the rear elevational view, left-side elevational view, and right-side elevational view all being identical thereto; and,
FIG. 3 is a top plan view thereof, the bottom plan view being a mirror image thereof.
The broken lines showing a support in FIG. 1 depict environmental matter and form no part of the claimed design.