crashtesting: assert on import of ooo96040-1.odt

 #0  std::__uniq_ptr_impl<sw::MergedPara, std::default_delete<sw::MergedPara> >::_M_ptr (this=0x108)
     at include/c++/8.2.0/bits/unique_ptr.h:150
 #1  0x00007f759b5ef71e in std::unique_ptr<sw::MergedPara, std::default_delete<sw::MergedPara> >::get (this=0x108)
     at include/c++/8.2.0/bits/unique_ptr.h:343
 #2  0x00007f759b870d00 in SwTextFrame::GetMergedPara (this=0x0) at sw/source/core/inc/txtfrm.hxx:437
 #3  0x00007f759be822f9 in sw::GetAttrMerged (rFormatSet=SfxItemSet of pool 0x4aae540 with parent 0x0 and Which ranges: [(68, 68), (90, 91)] = {...},
     rNode=..., pLayout=0x4b6f490) at sw/source/core/text/txtfrm.cxx:378
 #4  0x00007f759bf47a53 in SwTextNode::GetParaAttr (this=0x51bf980,
     rSet=SfxItemSet of pool 0x4aae540 with parent 0x0 and Which ranges: [(68, 68), (90, 91)] = {...}, nStt=0, nEnd=0, bOnlyTextAttr=false,
     bGetFromChrFormat=true, bMergeIndentValuesOfNumRule=true, pLayout=0x4b6f490)
     at sw/source/core/txtnode/thints.cxx:2072
 #5  0x00007f759baea5cc in SwEditShell::GetPaMAttr (this=0x50e7050, pPaM=0x4b42e38,
     rSet=SfxItemSet of pool 0x4aae540 with parent 0x0 and Which ranges: [(68, 68), (90, 91)] = {...}, bMergeIndentValuesOfNumRule=true)
     at sw/source/core/edit/edattr.cxx:144
 #6  0x00007f759baea772 in SwEditShell::GetCurAttr (this=0x50e7050,
     rSet=SfxItemSet of pool 0x4aae540 with parent 0x0 and Which ranges: [(68, 68), (90, 91)] = {...}, bMergeIndentValuesOfNumRule=true)
     at sw/source/core/edit/edattr.cxx:184
 #7  0x00007f759c733449 in SwView::StateTabWin (this=0x4e28f10,
     rSet=SfxItemSet of pool 0x4aae540 with parent 0x0 and Which ranges: [(10082, 10082), (10084, 10084), (10415, 10415)] = {...})
     at sw/source/uibase/uiview/viewtab.cxx:1234
 #8  0x00007f759c6f8c83 in SfxStubSwViewStateTabWin (pShell=0x4e28f10,
     rSet=SfxItemSet of pool 0x4aae540 with parent 0x0 and Which ranges: [(10082, 10082), (10084, 10084), (10415, 10415)] = {...})
     at workdir/SdiTarget/sw/sdi/swslots.hxx:13525

Change-Id: I126a043ad3dc274da629a9a4efe349eafd85b485
Reviewed-on: https://gerrit.libreoffice.org/66326
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>

sw/source/core/text/txtfrm.cxx

@@ -374,8 +374,8 @@ namespace sw {
         rNode.SwContentNode::GetAttr(rFormatSet);
         if (pLayout && pLayout->IsHideRedlines())
         {
-            if (sw::MergedPara const*const pMerged =
-                static_cast<SwTextFrame*>(rNode.getLayoutFrame(pLayout))->GetMergedPara())
+            auto pFrame = static_cast<SwTextFrame*>(rNode.getLayoutFrame(pLayout));
+            if (sw::MergedPara const*const pMerged = pFrame ? pFrame->GetMergedPara() : nullptr)
             {
                 if (pMerged->pFirstNode != &rNode)
                 {