tdf#124586 sw_redlinehide: fix crash in SwTextNode::NumRuleChgd()

(regression from c180c944)

Change-Id: Ie3c935ee5dd42187ca8ad2b28406b80e63c0d1e3
Reviewed-on: https://gerrit.libreoffice.org/70467Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
Tested-by: Michael Stahl <Michael.Stahl@cib.de>
(cherry picked from commit 7587e390)
Reviewed-on: https://gerrit.libreoffice.org/70500
Tested-by: Jenkins
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>

sw/source/core/txtnode/ndtxt.cxx

@@ -2864,7 +2864,10 @@ void SwTextNode::NumRuleChgd()
         if ( pNumRule && pNumRule != GetNum()->GetNumRule() )
         {
             mpNodeNum->ChangeNumRule( *pNumRule );
-            mpNodeNumRLHidden->ChangeNumRule( *pNumRule );
+            if (mpNodeNumRLHidden)
+            {
+                mpNodeNumRLHidden->ChangeNumRule(*pNumRule);
+            }
         }
     }