The ornamental design for a cover for a stadiumseat, as shown and described.
FIG. 1 is a perspective view of a cover for a stadium seat according to the invention.
FIG. 2 is a front, elevation view of the cover.
FIG. 3 is a rear, elevation view of the cover.
FIG. 4 is a right side, elevation view of the cover.
FIG. 5 is a left side, elevation view of the cover.
FIG. 6 is a top, plan view of the cover.
FIG. 7 is a bottom, plan view of the cover; and,
FIG. 8 is another perspective view of the cover.
The broken lines in FIGS. 1-8 showing other structure of the cover and other structure of the stadium seat are illustrative of environmental structure only and do not form a part of the claimed design.