use _safe_single_attr wrapper also for the map qualities
Work around issue in pysam when handling tabix inputs with large numbers of blank columns, which occurs when annotating with results from VEP: https://github.com/pysam-developers/pysam/pull/44
Merge pull request #333 from bgruening/fix_get_map_qual_zero

use _safe_single_attr wrapper also for the map qualities
Avoid picking up empty extra files for post-GEMINI annotation