protect against missing SuperTable

Change-Id: I788ec28424bb638f727901b7d25e48a284ab67d0
(cherry picked from commit 356109d4)
Reviewed-on: https://gerrit.libreoffice.org/20507Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

lotuswordpro/source/filter/lwpfribtable.cxx

@@ -97,6 +97,8 @@ void LwpFribTable::XFConvert(XFContentContainer* pCont)
 {
     XFContentContainer* pXFContentContainer = pCont;
     LwpSuperTableLayout* pSuper = GetSuperTable();
+    if (!pSuper)
+        return;
     sal_uInt8 nType = pSuper->GetRelativeType();
     LwpVirtualLayout* pContainer = pSuper->GetContainerLayout();
     if (!pContainer)