As detected by @mikael-s in the parent commit, the region between V and J affectations
was not taken into account in the p-values, yielding erroneous segmentations
when this region was very large.

Now this region is counted *both* for the computation of left and right p-values, solving
the bug of the parent commit.

This could be sometimes over-conservative : are we counting things twice ?
In regular situations, the answer is no, as the p-values
are eventually computed by getProbabilityAtLeastOrAbove in kmerstore.h,
that takes into account the length of the seed.

A more exact option could have been to use something like
(first_pos_max + last_pos_max / 2) + getS()/2, but it would raise symmetry problems.
The selected option should anyway improve the estimation in most of the cases.