Avoid returning 404 if there is no coverage

Author: talavis

backend/modules/browser/lookups.py

@@ -163,8 +163,6 @@ def get_coverage_for_bases(dataset: str, chrom: str, start_pos: int,
                            (db.Coverage.chrom == chrom) &
                            (db.Coverage.dataset_version == dataset_version.id))
                     .dicts())
-    if not coverage:
-        raise error.NotFoundError('No coverage found for the region')
     return coverage