Fix bug when no tardinesses exist

aleksis/apps/alsijil/templatetags/time_helpers.py

@@ -8,7 +8,7 @@ register = template.Library()
 @register.filter("to_time")
 def get_time_from_minutes(minutes: int) -> datetime.timedelta:
     """Get a time object from a number of minutes."""
-    delta = datetime.timedelta(minutes=minutes)
+    delta = datetime.timedelta(minutes=(minutes or 0))
     time_obj = (datetime.datetime.min + delta).time()
 
     return time_obj