fix: compute version rank while unfurling vers

Signed-off-by: Keshav Priyadarshi <git@keshav.space>

Author: keshav-space

vulnerabilities/pipelines/v2_improvers/unfurl_version_range.py

@@ -166,7 +166,10 @@ def bulk_create_with_m2m(purls, impact, relation, logger):
 
     affected_packages_v2 = PackageV2.objects.bulk_get_or_create_from_purls(purls=purls)
 
-    affected_packages_v2[-1].calculate_version_rank
+    if not affected_packages_v2:
+        return 0
+
+    affected_packages_v2.first().calculate_version_rank
 
     relations = [
         relation(impacted_package=impact, package=package) for package in affected_packages_v2