Mark CVE-2019-8937 as fixed in unstable

Marco De Santis (upstream) of hoteldruid confirmed in #929136 that the
issues covered by CVE-2019-8937 are adressed as well already in 2.3.2.

When checking I did not found at least the change for nsextt but that
might have been an oversight on my end. Follow the upstream confirmation
and mark it as fixed in 2.3.2-1.