Just a little refactoring.

Gets rid of the common used idom in the code:
  m_pTopLevel ? m_pTopLevel : m_pQWidget

Change-Id: I3e96687d9d02c0b1a5537c6b6cea53e1ca3a2067
Reviewed-on: https://gerrit.libreoffice.org/73414
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>