`ItemStackView`s may take up `InventoryView`'s whole rect

[don-tnowe]

• Happens only to some inventories - other views with same base type (e. g. Control or MarginContainer)
• _redraw_item() on all items doesn't help, even if deferred
• Grabbing any item stack from affected inventory fixes it.

Steps to reproduce

• ¯\(ツ)/¯

This does occur in example, commit 312ddf1bd67338c9adf33a28a73ab407c9e2490f :

• Open inventory
• Place any potions in the potion section of the equip tab
• Close inventory then close game preview
• Restart preview
• Open inventory's equip tab

Equipment, ammo and currency inventories are fine, while Potion views will be stretched.

[don-tnowe]

Update: this happens if the "Cells" node is a container, but not if it's a base Control. The children of the "Cells" node start at the wrong size, the stack views get their rect set from those wrong sizes. Presumably, they're correct next frame, but the stack views were already repositioned.

After putting call_deferred() everywhere, I decided to use await and looks like you need to wait for visibility_changed then process_frame. sort_children, weirdly, doesn't work even if you wait a frame.