which prevents destructor from being called. It was ScFormulaDlg's
own m_aHelper member variable holding reference to 'this'
(extra-wicked, through SetWindow(this)), never releasing it.

Change-Id: I258a280e09674d1a2f1ddebea19ea1b42dcdc777
Reviewed-on: https://gerrit.libreoffice.org/17954Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>