sw: layout: fix crash when deleting page with section being formatted

This crashes only when calling storeToURL() with writer_pdf_Export?

There is a text frame 112, followed by section frame 126, which contains
table frame 127.

The section frame 126 is being formatted, which in
SwFrame::PrepareMake() formats its prev, text frame 112.

This does MoveBwd() and in SwContentFrame::MakeAll() formats its next,
tab frame 127.

This also does MoveBwd() and then there is this really odd condition in
SwTabFrame::Paste() where it calls SwFrame::CheckPageDescs() if it
*doesn't* have a RES_PAGEDESC item and the page has a non-default page
style - this condition remains inexplicable since initial CVS import.

Then CheckPageDesc() sees the (next) page is empty and deletes it.

So check in sw::IsPageFrameEmpty() that there aren't any sections with
IsDeleteForbidden() set.

(regression from commit b9ef71476f)

Change-Id: I3c64fe40fabffc255c4146a35c678ce6a1cc09c9
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/133222
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@allotropia.de>

sw/source/core/inc/layfrm.hxx

@@ -100,6 +100,7 @@ public:
                         SwPrintData const*const pPrintData = nullptr ) const override;
     const SwFrame *Lower() const { return m_pLower; }
           SwFrame *Lower()       { return m_pLower; }
+    bool ContainsDeleteForbiddenLayFrame() const;
     const SwContentFrame *ContainsContent() const;
     inline SwContentFrame *ContainsContent();
     const SwCellFrame *FirstCell() const;

sw/source/core/layout/findfrm.cxx

@@ -165,6 +165,27 @@ const SwFrame *SwLayoutFrame::ContainsAny( const bool _bInvestigateFootnoteForSe
     return nullptr;
 }
 
+bool SwLayoutFrame::ContainsDeleteForbiddenLayFrame() const
+{
+    if (IsDeleteForbidden())
+    {
+        return true;
+    }
+    for (SwFrame const* pFrame = Lower(); pFrame; pFrame = pFrame->GetNext())
+    {
+        if (!pFrame->IsLayoutFrame())
+        {
+            continue;
+        }
+        SwLayoutFrame const*const pLay(static_cast<SwLayoutFrame const*>(pFrame));
+        if (pLay->ContainsDeleteForbiddenLayFrame())
+        {
+            return true;
+        }
+    }
+    return false;
+}
+
 const SwFrame* SwFrame::GetLower() const
 {
     return IsLayoutFrame() ? static_cast<const SwLayoutFrame*>(this)->Lower() : nullptr;

sw/source/core/layout/pagechg.cxx

@@ -1026,6 +1026,8 @@ bool IsPageFrameEmpty(SwPageFrame const& rPage)
          rPage.FindFootnoteCont() ||
          (nullptr != (pBody = rPage.FindBodyCont()) &&
             ( pBody->ContainsContent() ||
+              // check for section frames that are being formatted on the stack
+              rPage.ContainsDeleteForbiddenLayFrame() ||
                 // #i47580#
                 // Do not delete page if there's an empty tabframe
                 // left. I think it might be correct to use ContainsAny()