Resolves: tdf#130541 null-deref on detaching already-detached page

Change-Id: Ib48ab91232b8ff624a1387ab82701938eef58ded
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/88380
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>

extensions/source/propctrlr/browserpage.cxx

@@ -32,7 +32,9 @@ namespace pcr
 
     OBrowserPage::~OBrowserPage()
     {
-        m_pParent->move(m_xContainer.get(), nullptr);
+        if (m_pParent)
+            detach();
+        assert(!m_pParent);
     }
 } // namespace pcr