insertions in LocusIterator bugfix

[nkarulin]

The current version of AbstractLocusIterator class works the following way: when new read comes, it completes all accumulated loci with position to the left of the read start. When the flag includeIndels is specified, the read starting with insertions won't complete the locus at the position to the left of the read start. So, iterator will keep previous locus, which will store insertion info.
The bug appears when a read that does not start with insertion(REC1) comes before the read that does start with insertion (REC2) at the same position:

REF                     :  ATGC....TGCATGCATGC
REC (Pos=5, CIGAR: 3M)  :          TGC
REC (Pos=5, CIGAR: 3I3M):      TGCATGC

In this case the first read without insertion will complete all loci at the previous positions. As a result there is no locus in which we should have accumulated the insertion from the second read which leads to IllegalStateException.
We propose to store one more locus in accumulator before completion to make sure that all records (including those that start with insertion) on current position were accumulated.