apparatus_converter: fallback if no forename is found

I got an IndexError on Mondrian data, possibly due to invalid input

Author: proycon

editem_apparatus/apparatus_converter.py

@@ -334,7 +334,11 @@ def _preferred_pers_name(pers_names: Union[dict[str, Any], list[dict[str, Any]]]
                 if "forename" in abb:
                     return abb
                 else:
-                    return [pn for pn in pers_names if "forename" in pn][0]
+                    try:
+                        return [pn for pn in pers_names if "forename" in pn][0]
+                    except IndexError:
+                        #fallback
+                        return abb
             else:
                 return pers_names[0]