Only get new items where no previous hash error.

src/bin/load_hashes.rs

@@ -74,6 +74,7 @@ async fn main() {
                     post
                 WHERE
                     hash IS NULL AND
+                    hash_error IS NULL AND
                     data->>'file_ext' IN ('jpg', 'png') AND
                     data->>'file_url' <> '/images/deleted-preview.png'
                 LIMIT 100",