- since List is being used to manage the storage content for
  DynamicList, it needs to free old memory for zero-sized lists first.

  Consider this case (slightly exaggerated):

      line 0:  DynamicList<label> list;
      line 1:  list.reserve(100000);
      line 2:  list.reserve(200000);

  After line 0:
     - list has size=0, capacity=0 and data=nullptr

  After line 1:
     - list has size=0, capacity=1e+5 and data != nullptr

  After line 2:
     - list has size=0, capacity=2e+5 and data != nullptr

  ---

  The internal resizing associated with line 1 corresponds to what the
  List resize would naturally do. Namely allocate new storage, copy/move
  any overlapping elements (in this case none) before freeing the old
  storage and replacing with new storage.

  Applying the same resizing logic for line 2 means, however, that the
  old memory (1e5) and new memory (2e5) are temporarily both
  accessible - leading to an unnecessary memory peak.

  Now: if there is no overlap, just remove old memory first.