fdo#55814 SwDoc::UpdateExpFlds: hiding the last section may be safe

In case we know there is a non-section paragraph at the end of the
document.  Intentionally not adding a unit test as David Ostrovsky is
working on one already.

(cherry picked from commit 62344016)

Change-Id: Ia6026846981b5af014246a8a604c5f762d34c891
Reviewed-on: https://gerrit.libreoffice.org/2876Reviewed-by: David Ostrovsky <David.Ostrovsky@gmx.de>
Tested-by: David Ostrovsky <David.Ostrovsky@gmx.de>

sw/source/core/doc/docfld.cxx

@@ -1304,10 +1304,16 @@ void SwDoc::UpdateExpFlds( SwTxtFld* pUpdtFld, bool bUpdRefFlds )
                     // This section will be hidden, but it wasn't before
                     if (nShownSections == 1)
                     {
-                        // This would be the last section, so set its condition to false, and avoid hiding it.
-                        OUString aCond("0");
-                        pSect->SetCondition(aCond);
-                        bHide = false;
+                        // Is the last node part of a section?
+                        SwPaM aPam(GetNodes());
+                        aPam.Move(fnMoveForward, fnGoDoc);
+                        if (aPam.Start()->nNode.GetNode().StartOfSectionNode()->IsSectionNode())
+                        {
+                            // This would be the last section, so set its condition to false, and avoid hiding it.
+                            OUString aCond("0");
+                            pSect->SetCondition(aCond);
+                            bHide = false;
+                        }
                     }
                     nShownSections--;
                 }