Multiple problems with the memory handler regarding unused entities

[SleepProgger]

1. The memory_handler.utils.memrange_iter doesn't properly handle freed entities.
   It is casting the void pointer to unsigned int and checks for -1 instead of using the value located at that pointer address. That one is simple to fix like:

        ...
        cdef unsigned int* pointer
        if current >= self.end:
            raise StopIteration
        else:
            pool_index = memory_zone.get_pool_index_from_index(current)
            used = memory_zone.get_pool_end_from_pool_index(pool_index)
            if current >= used:
                self.current = memory_zone.get_pool_range(pool_index)[1] + 1
                return next(self)
            else:
                pointer = <unsigned int*>memory_zone.get_pointer(current)
                self.current += 1
                if pointer[0] == <unsigned int>-1:
                    return next(self)
            ...

2. The python side of things has a somewhat related problem as StaticMemGameSystem.components returns entities that a) have the entity_id set to -1 (were once used and are freed atm) and b) also returns never used entities (the entity_id and everything else being 0).
   IMHO in both cases the python side of things should get a None.
   I am not sure how to handle this one. One way would be to initially set every entity_id to -1, but it would propably be nicer to simple not return never used entites (which as far as i understand can only be entities on the tail anyway).