avoid crash on layout of ooo77837-1.odt

by attempting to set the parent as un-joinable for the duration of the
Cut/Paste in order to ensure it survives the process

==14185== Invalid read of size 8
==14185==    at 0x27AB1CF4: SwLayoutFrm::Lower() (layfrm.hxx:108)
==14185==    by 0x27FE3FD4: SwFlowFrm::PasteTree(SwFrm*, SwLayoutFrm*, SwFrm*, SwFrm*) (flowfrm.cxx:455)
==14185==    by 0x27FE4597: SwFlowFrm::MoveSubTree(SwLayoutFrm*, SwFrm*) (flowfrm.cxx:584)
==14185==    by 0x2801CF8B: SwCntntFrm::MoveFtnCntFwd(bool, SwFtnBossFrm*) (ftnfrm.cxx:2753)
==14185==    by 0x27FE7C29: SwFlowFrm::MoveFwd(bool, bool, bool) (flowfrm.cxx:1795)

==14185==  Address 0x11a74da8 is 168 bytes inside a block of size 288 free'd
==14185==    by 0x2808CAC8: SwSectionFrm::~SwSectionFrm() (sectfrm.cxx:153)
==14185==    by 0x2808DCC5: SwSectionFrm::MergeNext(SwSectionFrm*) (sectfrm.cxx:453)
==14185==    by 0x2808EC4B: SwSectionFrm::MakeAll() (sectfrm.cxx:713)
==14185==    by 0x27FCD000: SwFrm::PrepareMake() (calcmove.cxx:306)
==14185==    by 0x27DCAAC1: SwFrm::Calc() const (frame.hxx:996)
==14185==    by 0x27FE3EB9: SwFlowFrm::CutTree(SwFrm*) (flowfrm.cxx:418)
==14185==    by 0x27FE4577: SwFlowFrm::MoveSubTree(SwLayoutFrm*, SwFrm*) (flowfrm.cxx:583)
==14185==    by 0x2801CF8B: SwCntntFrm::MoveFtnCntFwd(bool, SwFtnBossFrm*) (ftnfrm.cxx:2753)
==14185==    by 0x27FE7C29: SwFlowFrm::MoveFwd(bool, bool, bool) (flowfrm.cxx:1795)

Change-Id: If96d845fdf22726df513b0dabd2764ad60c85987

sw/qa/extras/odfimport/odfimport.cxx

@@ -319,6 +319,11 @@ DECLARE_ODFIMPORT_TEST(testCalcFtnCntnt, "ooo32780-1.odt")
     //this was a CalcFtnCntnt crash
 }
 
+DECLARE_ODFIMPORT_TEST(testMoveSubTree, "ooo77837-1.odt")
+{
+    //this was a MoveSubTree crash
+}
+
 DECLARE_ODFIMPORT_TEST(testFdo75872_ooo33, "fdo75872_ooo33.odt")
 {
     // graphics default style: line color and fill color changed

sw/source/core/layout/flowfrm.cxx

@@ -574,9 +574,23 @@ void SwFlowFrm::MoveSubTree( SwLayoutFrm* pParent, SwFrm* pSibling )
 
     SwPageFrm *pOldPage = m_rThis.FindPageFrm();
 
+    //JoinLock pParent for the lifetime of the Cut/Paste call to avoid
+    //SwSectionFrm::MergeNext removing the pParent we're trying to reparent
+    //into
+    bool bOldJoinLocked(false);
+    SwFlowFrm *pParentFlow = SwFlowFrm::CastFlowFrm(pParent);
+    if (pParentFlow)
+    {
+        bOldJoinLocked = pParentFlow->IsJoinLocked();
+        pParentFlow->LockJoin();
+    }
+
     SwLayoutFrm *pOldParent = CutTree( &m_rThis );
     const bool bInvaLay = PasteTree( &m_rThis, pParent, pSibling, pOldParent );
 
+    if (pParentFlow && !bOldJoinLocked)
+        pParentFlow->UnlockJoin();
+
     // If, by cutting & pasting, an empty SectionFrm came into existence, it should
     // disappear automatically.
     SwSectionFrm *pSct;