Adding a separatorBuilder to the package's ListView example causes overlapping items

[Lewis Holliday]

The argument passed to SliverExpandableChildDelegate:
separatorBuilder: (context, isHeader, index) { return Container(); },

Steps to reproduce:

1. Expand some headers (Including header 0 and header 1 to allow scrolling.
2. Close Header 0
3. Expand Header 0
4. Scroll down
   This will make header 1's items overlap with header 0

Visual:

Tested on:
Flutter 2.5.3, sticky_and_expandable_list: 1.0.2,
Android phone and Chrome.

[tp7309]

thank you for your feedback, fixed at v1.0.3.