Fix error handling and messages in move_dates_for_testing

aleksis/apps/untis/management/commands/move_dates_for_testing.py

@@ -65,7 +65,7 @@ class Command(BaseCommand):
         school_terms = SchoolTerm.objects.order_by("-date_end")
 
         if not school_terms.exists():
-            raise RuntimeError("No validity range available.")
+            raise RuntimeError("No school term available.")
 
         school_term = school_terms.first()
         self.stdout.write(f"Used school term: {school_term}")
@@ -90,7 +90,8 @@ class Command(BaseCommand):
         )
 
         if not self.weeks:
-            raise RuntimeError("You need at least one validity range to move data.")
+            self.stdout.write(self.style.ERROR("There are no data that have to be moved."))
+            return
 
         self.translate_week_year(
             "SUBSTITUTIONS",