Scroll in the graph widget disappears with a large number of items/hosts

 Steps to reproduce:

1. Add new graph widget
2. Select all items from Zabbix servers in item multiselect input for first data set (should be many items and scroll in widget)
3. Collapse first data set
4. Press on button "Add new data set"
5. Click on host multiselect input in first data set

Result:
First data set expands, but scroll doesn't appear in widget
Expected:
Able to scroll in widget