only try to open the alignments file if it is defined and exists.
only try to open the alignments file if it is defined and exists.

EichlerLab/pacbio_variant_caller,EichlerLab/pacbio_variant_caller,EichlerLab/pacbio_variant_caller,EichlerLab/pacbio_variant_caller,EichlerLab/pacbio_variant_caller