The ornamental design for a frontcover of a display device, as shown and described.
FIG. 1 is a front perspective view of a front cover of a display device, such as a head mounted display, a virtual reality display, an augmented reality display, or a mixed reality display, in accordance with our new design;
FIG. 2 is a another front perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a left view thereof;
FIG. 5 is a right view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
There is no design feature to be shown in the rear views of the front cover, and thus the rear views of the front cover are omitted therein. The broken lines in the drawings depict parts of the front cover of a display device only and form no part of the claimed design.