Revert "[FIX] FM index: do not compute prefix sums twice when constructing the index"
Revert "[FIX] FM index: do not compute prefix sums twice when constructing the index"

This reverts commit abc5e2f74795dec4ca87feefeae4d66f624bdb02.

bestrauc/seqan,bestrauc/seqan,xenigmax/seqan,bestrauc/seqan,xenigmax/seqan,bestrauc/seqan,bestrauc/seqan,xenigmax/seqan,xenigmax/seqan,xenigmax/seqan,xenigmax/seqan,xenigmax/seqan,xenigmax/seqan,bestrauc/seqan,bestrauc/seqan,bestrauc/seqan