[ENSCORESW-922]. Problem with circular chromosomes when feature start/end wrt slice are negative.
The computation of min_start/max_end is not reliable in this case.
Can safely use seq_region_start/end since these are fetched from the DB in the circular slice case.
There's no problem even when there are features with seq_region_start > seq_region_end since these
are not directly compared.
[ENSCORESW-922]. Can use the same code fragment for both circular/non-circular chromosomes.