MemoryHabitList: iterate over a copy of the list

uhabits-core/src/main/java/org/isoron/uhabits/core/models/memory/MemoryHabitList.java

@@ -164,7 +164,7 @@ public class MemoryHabitList extends HabitList
     @Override
     public synchronized Iterator<Habit> iterator()
     {
-        return Collections.unmodifiableCollection(list).iterator();
+        return new ArrayList<>(list).iterator();
     }
 
     @Override