ingest: Filter out empty host "Query"

Since we need to join the host taxonomy info with the metadata via
the "Query" key, filter out lines where the "Query" column is empty.

This is also a work-around that resolves
<#17>.

ingest/rules/fetch_from_ncbi.smk

@@ -146,6 +146,7 @@ rule join_metadata_and_hostinfo:
     shell:
         """
         unzip -p {input.ncbi_hosttax_info} ncbi_dataset/data/taxonomy_summary.tsv \
+        | tsv-filter -H --not-blank Query \
         | tsv-select -H -f {params.ncbi_hosttax_columns} \
         | tsv-join -H \
         --filter-file - \