popup: fix sizing eval logic when scrollable set TRUE

popup: fix sizing eval logic when scrollable set TRUE

Summary:
When scrollable set TRUE,
scroller must be calculated its size except using item.
If content is removed, scroller doesn't calculate its size, so it has previous size.
So there is a empty space in this case.

@fix

Test Plan:
1. elementary_test -to popup
2. open "popup-center-title + list content + 2 button (with delete content)"
3. click "Delete" button
4. compare between scrollable set true and false

Reviewers: herb, singh.amitesh, jpeg, cedric, conr2d

Differential Revision: https://phab.enlightenment.org/D5010