fix: should always remove existing derived_from links

scripts/stac/imagery/create_stac.py

@@ -129,10 +129,11 @@ def create_item(
     if not gdalinfo_result:
         gdalinfo_result = gdal_info(asset_path)
 
-    if derived_from is not None:
+    if item.stac.get("links") is not None:
         # Remove existing derived_from links in case of resupply
         item.stac["links"] = [link for link in item.stac["links"] if link["rel"] != "derived_from"]
 
+    if derived_from is not None:
         for derived in derived_from:
             derived_item_content = read(derived)
             derived_stac = json.loads(derived_item_content.decode("UTF-8"))