Resolves: tdf#123694 we need the controller, not the tabpage parent

Change-Id: Ib390abaec648a1e06fcc35f83cb170fc654cf021
Reviewed-on: https://gerrit.libreoffice.org/69203
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

chart2/source/controller/dialogs/res_ErrorBar.cxx

@@ -41,8 +41,9 @@ namespace
 {
 void lcl_enableRangeChoosing(bool bEnable, TabPageParent pParent)
 {
-    if (weld::Window* pWeldDialog = dynamic_cast<weld::Window*>(pParent.pPage))
+    if (weld::DialogController* pController = pParent.pController)
     {
+        weld::Window* pWeldDialog = pController->getDialog();
         pWeldDialog->set_modal(!bEnable);
         pWeldDialog->show(!bEnable);
     }