when we're not recording undo, then SdrUndoDelObj just deletes
the argument its passed. And this code assumes that it is transferred
to the SdrUndoDelObj and it still exists.

Use the same pattern as ScPostIt::RemoveCaption for this situation

Invalid read of size 8
   at 0xB1713B6: SdrObject::GetOrdNum() const (svdobj.cxx:777)
   by 0x3C9E029C: ScDetectiveFunc::DeleteArrowsAt(short, int, bool) (detfunc.cxx:695)
   by 0x3C9E1D4C: ScDetectiveFunc::FindSuccLevel(short, int, short, int, unsigned short, unsigned short) (detfunc.cxx:1118)
   by 0x3C9E2405: ScDetectiveFunc::DeleteSucc(short, int) (detfunc.cxx:1207)
   by 0x3CF812BA: ScDocFunc::DetectiveRefresh(bool) (docfunc.cxx:480)
   by 0x3CFC9FAF: ScDocShell::DoHardRecalc(bool) (docsh4.cxx:1250)

 Address 0x50992d50 is 112 bytes inside a block of size 464 free'd
   at 0x4C2D22A: operator delete(void*) (vg_replace_malloc.c:576)
   by 0xB1D04BC: SdrPathObj::~SdrPathObj() (svdopath.cxx:1681)
   by 0xB1701F5: SdrObject::Free(SdrObject*&) (svdobj.cxx:394)
   by 0xB258666: SdrUndoObjList::~SdrUndoObjList() (svdundo.cxx:720)
   by 0xB258A39: SdrUndoRemoveObj::~SdrUndoRemoveObj() (svdundo.cxx:774)
   by 0xB25E29B: SdrUndoDelObj::~SdrUndoDelObj() (svdundo.hxx:298)
   by 0xB25E2B7: SdrUndoDelObj::~SdrUndoDelObj() (svdundo.hxx:298)
   by 0x3C7E5D0E: ScDrawLayer::AddCalcUndo(SdrUndoAction*) (drwlayer.cxx:1120)
   by 0x3C9E0238: ScDetectiveFunc::DeleteArrowsAt(short, int, bool) (detfunc.cxx:692)

Change-Id: Idc6d1f8e9ad8b203dac55630f8c100e74d3e017b