tdf#130680 sw_redlinehide: fix crash in SwUndoDelete

The problem is that the code that adjusts pLastNode in
SwContentNode::DelFrames() assumes that the nodes are deleted forward
but MoveNode() runs backward so the only solution is to put pLastNode
temporarily onto some node without checking if it has been fully
deleted, while skipping over tables and sections.

At the end of MoveNode() it must be on a valid (not fully deleted) node
again.

(regression from b86ff2c6a88aa41379e74f11e8ec8497ff85ffd0)

Change-Id: If54c01f885e0c040aed9068823deae7dd167fd50
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/89896
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@cib.de>
(cherry picked from commit 4769f431d93139eb3c470e5bb4e7c3c33d46a41f)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/89910
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>
diff --git a/sw/source/core/docnode/node.cxx b/sw/source/core/docnode/node.cxx
index 7ecaa51..37083c1 100644
--- a/sw/source/core/docnode/node.cxx
+++ b/sw/source/core/docnode/node.cxx
@@ -1386,15 +1386,26 @@ void SwContentNode::DelFrames(SwRootFrame const*const pLayout)
                            }
                        }
                    }
                    assert(GetIndex() <= pMerged->pLastNode->GetIndex());
                    if (this == pMerged->pLastNode)
                    {
                        pMerged->pLastNode = GetNodes()[GetIndex()-1]->GetTextNode();
                        // at first glance nothing guarantees this...
                        // but the redline must end on a text-node...
                        // so everything before this node that isn't a text
                        // node should have been deleted already so that
                        // there's a text node before.
                        assert(pMerged->pLastNode->IsTextNode());
                        // tdf#130680 find the previous node that is a
                        // listener of pMerged; see CheckParaRedlineMerge()
                        for (sal_uLong i = GetIndex() - 1;
                             this == pMerged->pLastNode; --i)
                        {
                            SwNode *const pNode = GetNodes()[i];
                            if (pNode->IsTextNode())
                            {
                                pMerged->pLastNode = pNode->GetTextNode();
                            }
                            else if (SwEndNode const*const pEnd = pNode->GetEndNode())
                            {
                                SwStartNode const*const pStart(pEnd->StartOfSectionNode());
                                i = pStart->GetIndex(); // skip table or section
                            }
                        }
                        assert(pMerged->pFirstNode->GetIndex() <= pMerged->pLastNode->GetIndex());
                    }
                    // avoid re-parenting mess (ModifyChangedHint)
                    pMerged->listener.EndListening(this);