格子のセルの数を読み込む。
call cg_iric_read_grid_cellcount_withgridid(fid, gid, count, ier)
ier = cg_iRIC_Read_Grid_CellCount_WithGridId(fid, gid, &count);
count = cg_iRIC_Read_Grid_CellCount_WithGridId(fid, gid)