In preparation of forward-porting the distro/collabora/cp-6.0-only
commit 418adc09 (lo: disable under-used
hyperlink fields that are buggy online., 2019-05-22), which relaxes the
invariant that mpLbForm never returns LISTBOX_ENTRY_NOTFOUND.
A signed integer overflow is a problem in itself, but in practice the
SID_HYPERLINK_SETLINK handler in sd::DrawViewShell::FuTemporary() didn't
insert a field, since the insert mode was a large negative value instead
Reviewed-on: https://gerrit.libreoffice.org/73034Reviewed-by: Miklos Vajna <email@example.com>