Correctly validate CourseMap getters

[vabold]

Currently, we have:

MapdataStartPoint *CourseMap::getStartPoint(u16 i) const {
    return m_startPoint && m_startPoint->size() != 0 ? m_startPoint->get(i) : nullptr;
}

In reality, this is calling an inlined function to get the count of MapdataStartPoint instances in the accessor, which should look like this:

u16 CourseMap::getStartPointCount() const {
    return m_startPoint ? m_startPoint->size() : 0;
}

And in the base game, we should be comparing i against this count:

MapdataStartPoint *CourseMap::getStartPoint(u16 i) const {
    return i < getStartPointCount() ? m_startPoint->get(i) : nullptr;
}