Fix QC for single-locus data sets
Fix QC for single-locus data sets

Currently QC step 2 crashes when processing data which only contains
reads from a single valid locus. This is due to R's default behavior
to simplify single matrix columns to vectors, which also discards
the colnames. Suppress conversion, maintain single-column matrix.

b-cell-immunology/sciReptor,b-cell-immunology/sciReptor,b-cell-immunology/sciReptor,b-cell-immunology/sciReptor