Prevent repetition freelist bottom-out

It is not sufficient to know how many iterations will be needed at the
end of the next draw.  It is necessary to track whether enough
iterations will be available when an Add Operation is drawn.

This fixes the case where:

1.  N iterations are added (N iterations needed)
2.  N iterations are deleted (0 iterations needed, N max iterations
    needed)
3.  iteration template becomes available
4.  draw N iterations (free list is potentially empty)
5.  erase N iterations