The ornamental design for a fencepost, as shown and described.
FIG. 1 is a front perspective view of a fence post;
FIG. 2 is a rear perspective view of the fence post;
FIG. 3 is a view from one end of the fence post;
FIG. 4 is a view from one side of the fence post;
FIG. 5 is a front view of the fence post;
FIG. 6 is a view from an opposing end of the fence post;
FIG. 7 is a rear view of the fence post; and,
FIG. 8 is a view from an opposing side of the fence post.
The fence post is shown with a symbolic break in its length. The appearance of any portion of the article between the break lines forms no part of the claimed design.