The ornamental design for a wallblock, as shown and described.
FIG. 1 is a perspective view of the wall block;
FIG. 2 is a top view of the wall block;
FIG. 3 is a front view of the wall block;
FIG. 4 is a right side view of the wall block;
FIG. 5 is a rear view of the wall block;
FIG. 6 is a left side view of the wall block; and,
FIG. 7 is a top view of the wall block in its environment shown in broken lines.
The broken lines showing the other like blocks in FIG. 7 represent the environments. In all drawing views, the broken lines immediately adjacent the shaded areas represent the bounds of the claim, and all other broken lines are included for the purpose of illustrating portions of the wall block that form no part of the claimed design. None of the broken lines form no part of the claimed design.