aggr.py: made removal of staff (legi 00-000-000) slightly more robust

mossutils/aggr.py

@@ -47,7 +47,9 @@ def aggregate(
   course_csv = course_csv[relevant_course_columns]
   course_csv["TotalScore"] = course_csv["TotalScore"].round(0)
   course_csv.set_index("Legi", inplace=True)
-  course_csv.drop("00-000-000", inplace=True) ## NOTE: We assume that this indicates staff
+  course_csv.drop("00-000-000", errors="ignore", inplace=True)
+    ## NOTE: We assume that legi 00-000-000 indicates staff
+    ## error="ignore" prevents an exception in case the legi doesn't occur
 
   duplicated_indices: pd.Index = course_csv[course_csv.index.duplicated()].index
   assert \