sw: try to fix a valgrind warning

Invalid read of size 1
   at SwParaPortion::SetPrep(bool) (porlay.hxx:299)
   by SwTxtFrm::Prepare(PrepareHint, void const*, bool) (txtfrm.cxx:1756)
   by SwTxtFrm::Prepare(PrepareHint, void const*, bool) (txtfrm.cxx:1663)
   by SwCntntFrm::MakeAll() (calcmove.cxx:1310)
   by SwFrm::OptPrepareMake() (calcmove.cxx:356)
   by SwFrm::OptCalc() const (frame.hxx:1037)
   by SwLayAction::_FormatCntnt(SwCntntFrm const*, SwPageFrm const*) (layact.cxx:1829)
   by SwLayAction::FormatCntnt(SwPageFrm const*) (layact.cxx:1660)
   by SwLayAction::InternalAction() (layact.cxx:597)
   by SwLayAction::Action() (layact.cxx:376)
   by SwLayIdle::SwLayIdle(SwRootFrm*, SwViewImp*) (layact.cxx:2179)
 Address 0x1f9507e0 is 832 bytes inside a block of size 840 free'd
   by FixedMemPool::Free(void*) (mempool.cxx:48)
   by SwParaPortion::operator delete(void*, unsigned long) (in /work/lo/master/instdir/program/libswlo.so)
   by SwParaPortion::~SwParaPortion() (porlay.cxx:1972)
   by SwTxtFrm::ClearPara() (txtcache.cxx:102)
   by SwTxtFrm::Init() (txtfrm.cxx:329)
   by SwTxtFrm::CalcLineSpace() (txtfrm.cxx:746)
   by SwTxtFrm::Prepare(PrepareHint, void const*, bool) (txtfrm.cxx:1680)
   by SwTxtFrm::Prepare(PrepareHint, void const*, bool) (txtfrm.cxx:1663)
   by SwCntntFrm::MakeAll() (calcmove.cxx:1310)
   by SwFrm::OptPrepareMake() (calcmove.cxx:356)
   by SwFrm::OptCalc() const (frame.hxx:1037)
   by SwLayAction::_FormatCntnt(SwCntntFrm const*, SwPageFrm const*) (layact.cxx:1829)
   by SwLayAction::FormatCntnt(SwPageFrm const*) (layact.cxx:1660)
   by SwLayAction::InternalAction() (layact.cxx:597)
   by SwLayAction::Action() (layact.cxx:376)
   by SwLayIdle::SwLayIdle(SwRootFrm*, SwViewImp*) (layact.cxx:2179)

Change-Id: I64a1cc6ea301b653af951ba0e00e28d4655d2d97
fdo#78149: set the ViewPort even when painting to a MetaFile

ObjectContactOfPageView::DoProcessDisplay() has a special case for
painting to MetaFiles, and does not set the ViewPort from the passed-in
RedrawArea unless it's a printing or PDF export, with the result
that for a plain MetaFile all fly-frames in a Writer document
are painted, whether visible or not.

Since e2eda70f2746f08376d8cdf5e5360df217335aef now calls
GetPreviewMetaFile() after every document load, this issue is more
visible.

Since there is no obvious reason to ever ignore a passed RedrawArea,
simply always use it for the ViewPort, not just when printing.

Change-Id: I256710f1476181f567069b45a2a494b0d2064d6b