Also use the return value of the link's Call() [as the SvTreeListBox::ExpandingHdl()
is doing], the appropriate callbacks seem to return the expected 'false' in
the cases I've reviewed...

Change-Id: I0cdd63e8ec4c794839070b914150e0b32f743359
Reviewed-on: https://gerrit.libreoffice.org/51213Reviewed-by: pranavk <pranavk@collabora.co.uk>
Tested-by: pranavk <pranavk@collabora.co.uk>