internal/vulndbreqs: propagate non-nil error

The entryIterator wasn't returning a non-nil error in some cases.

Change-Id: Ic7cfbb89925fb61b53568832a1fba1842c9a2f1f
Reviewed-on: https://go-review.googlesource.com/c/pkgsite-metrics/+/484459
Reviewed-by: Zvonimir Pavlinovic <zpavlinovic@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Jonathan Amsterdam <jba@google.com>
diff --git a/internal/vulndbreqs/iterator.go b/internal/vulndbreqs/iterator.go
index d08326a..4d1f70a 100644
--- a/internal/vulndbreqs/iterator.go
+++ b/internal/vulndbreqs/iterator.go
@@ -62,6 +62,9 @@
 			it.it = nil
 			continue
 		}
+		if err != nil {
+			return nil, err
+		}
 		it.count++
 		return entry, nil
 	}