Fix buf in position setup without Elephant/Prince

Fix buf in position setup without Elephant/Prince

HaChu's check test assumes the piece after King in the piece list will be
Crown Prince. When positions without CP or DE (which causes addition of
a CP for promotion, marked as ABSENT) were loaded, this would not be the
case, and the presence of another piece could create the illusion of
immunity to check. In Chess / Shatranj / Makruk a dummy (ABSENT) CP was
added to prevent this, but the problem occurred just as much in set-up
positions of true Shogi variants. Now we always add a dummy CP if the
loaded position did not cause adding it already.