Update plate geometry for parallel build

gprMax/user_objects/cmds_geometry/plate.py

@@ -81,7 +81,13 @@ class Plate(RotatableMixin, GeometryUserObject):
         p3 = uip.round_to_grid_static_point(p1)
         p4 = uip.round_to_grid_static_point(p2)
 
-        _, p1, p2 = uip.check_box_points(p1, p2, self.__str__())
+        plate_within_grid, p1, p2 = uip.check_box_points(p1, p2, self.__str__())
+
+        # Exit early if none of the plate is in this grid as there is
+        # nothing else to do.
+        if not plate_within_grid:
+            return
+
         xs, ys, zs = p1
         xf, yf, zf = p2