Do not download images if they already exist

dan/datasets/extract/utils.py

@@ -40,6 +40,9 @@ class EntityType(NamedTuple):
 
 
 def download_image(element: Element, im_path: Path):
+    if im_path.exists():
+        return im_path
+
     tries = 1
     # retry loop
     while True: