We claim the ornamental design for an lamp cover, as shown and described.
FIG. 1 is a perspective view taken from the left side of the new design;
FIG. 2 is a top plan view thereof; and FIG. 3 is a front view thereof.
FIG. 4 is a side view thereof; FIG. 5 is a elevation plan view thereof;
and, FIG. 6 is a bottom plan view thereof. The broken lines are shown for
illustrative purposes only and form no part of the claimed design.