tdf#125751 sw: fix crash on formatting in SwLayoutFrame::PaintSwFrame()

It's less than ideal that the document is painted before being fully
formatted, but let's try to apply a band-aid...

0x6120001a97d0 is located 144 bytes inside of 280-byte region [0x6120001a9740,0x6120001a9858)
freed by thread T0 here:
    #1 SwFootnoteFrame::~SwFootnoteFrame() /home/ms/lo/master/sw/source/core/inc/ftnfrm.hxx:64:7
    #2 SwFrame::DestroyFrame(SwFrame*) sw/source/core/layout/ssfrm.cxx:389:9
    #3 SwContentFrame::Cut() sw/source/core/layout/wsfrm.cxx:1263:25
    #4 SwFlowFrame::MoveBwd(bool&) sw/source/core/layout/flowfrm.cxx:2544:17
    #5 SwContentFrame::MakeAll(OutputDevice*) sw/source/core/layout/calcmove.cxx:1522:17
    #6 SwFrame::PrepareMake(OutputDevice*) sw/source/core/layout/calcmove.cxx:366:5
    #7 SwFrame::Calc(OutputDevice*) const sw/source/core/layout/trvlfrm.cxx:1791:37
    #8 SwLayoutFrame::PaintSwFrame(OutputDevice&, SwRect const&, SwPrintData const*) const sw/source/core/layout/paintfrm.cxx:3328:17
    #9 SwLayoutFrame::PaintSwFrame(OutputDevice&, SwRect const&, SwPrintData const*) const sw/source/core/layout/paintfrm.cxx:3406:21
    #10 SwLayoutFrame::PaintSwFrame(OutputDevice&, SwRect const&, SwPrintData const*) const sw/source/core/layout/paintfrm.cxx:3406:21
    #11 SwRootFrame::PaintSwFrame(OutputDevice&, SwRect const&, SwPrintData const*) const sw/source/core/layout/paintfrm.cxx:3116:24
    #12 SwViewShell::Paint(OutputDevice&, tools::Rectangle const&) sw/source/core/view/viewsh.cxx:1840:34

(reportedly a regression from 18765b9fa739337d2d891513f6e2fb7c3ce23b50)

Change-Id: Iff5e783985c180b704b273fa26b7c498820640ac
Reviewed-on: https://gerrit.libreoffice.org/74749
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
diff --git a/sw/source/core/layout/paintfrm.cxx b/sw/source/core/layout/paintfrm.cxx
index a179b76..61898a8 100644
--- a/sw/source/core/layout/paintfrm.cxx
+++ b/sw/source/core/layout/paintfrm.cxx
@@ -3322,6 +3322,7 @@
    if ( !pFrame )
        return;

    SwFrameDeleteGuard g(const_cast<SwLayoutFrame*>(this)); // lock because Calc() and recursion
    SwShortCut aShortCut( *pFrame, rRect );
    bool bCnt = pFrame->IsContentFrame();
    if ( bCnt )