Fix bug when importing ref genome. s/if/elif.
Fix bug when importing ref genome. s/if/elif.

Bug introduced in d922023e8a1d4e7757bfa3e68aba3ace89f2a749.

churchlab/millstone,woodymit/millstone_accidental_source,woodymit/millstone_accidental_source,churchlab/millstone,churchlab/millstone,churchlab/millstone,woodymit/millstone,woodymit/millstone,woodymit/millstone_accidental_source,woodymit/millstone,woodymit/millstone_accidental_source,woodymit/millstone