Update information on CVE-2019-14493/opencv

The issue has bene fixed in upstream 4.1.1, but it's not 100% clear if
the issue affects as well the 3.x series. Similar code is present in
3.2.0+dfsg-6 in modules/core/src/persistence.cpp but the check might be
present there not having fully read checked through the code.

There was a refactoring later upstream, and the issue might have only
been present in this case in the 4.x series.