The ornamental design for a seatshelter, as shown and described.
FIG. 1 is a top perspective view of a seat shelter showing my new design;
FIG. 2 is a bottom perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left side thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top view thereof;
FIG. 8 is a bottom view thereof;
FIG. 9 is a cross-sectional top down view through the line 9-9 in FIG. 3; and,
FIG. 10 is a cross-sectional perspective view through the line 10-10 in the FIG. 3.
The broken lines in the figures are for the purpose of illustrating portions of the seat shelter, which form no part of the claimed design. The dash-dot broken lines in the figures are demarcating the section cuts and form no part of the claimed design.