Fix error in fix_up_custom_units caused by modifying a dictionary whi…

…le looping over its keys

webapp/home/utils/load_and_save.py

@@ -978,7 +978,7 @@ def collect_custom_units_from_additional_metadata(eml_node):
 
     # Remove any custom units from the additionalMetadata node that are not in the attributes, i.e., that are no longer
     #  needed.
-    current_keys = custom_units_from_additional_metadata.keys()
+    current_keys = list(custom_units_from_additional_metadata.keys())
     for key in current_keys:
         if key not in custom_units_from_attributes:
             del custom_units_from_additional_metadata[key]