guard against missing XFContentContainer

Change-Id: Ic974159f816bae465339e1b9abd2e247bbc2f206
(cherry picked from commit 0063b891)
(cherry picked from commit b2cc3858)
Reviewed-on: https://gerrit.libreoffice.org/20795Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>

lotuswordpro/source/filter/lwppara.cxx

@@ -880,7 +880,7 @@ void LwpPara::ParseDropcapContent()
  */
 void LwpPara::AddBreakBefore(XFContentContainer* pCont)
 {
-    if (!m_pBreaks)
+    if (!m_pBreaks || !pCont)
         return;
     if (m_pBreaks->IsPageBreakBefore())
     {