... so admit that the VclPtr that ChartController used to have is really
owned by m_xViewWindow, and get fetch that (stack-scoped only) from
there.

Change-Id: Ib9e2cd20201ebe5019c3607a8c65cb1a9856812f
Reviewed-on: https://gerrit.libreoffice.org/35603Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>