tdf#149280 modified called after dialog was destroyed

just ignore it in that case

Change-Id: I8f294acd9ee16d2f9c8662614fac3672f80b3376
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/134902
Tested-by: Jenkins
Reviewed-by: Xisco Fauli <xiscofauli@libreoffice.org>
diff --git a/desktop/source/deployment/gui/dp_gui_theextmgr.cxx b/desktop/source/deployment/gui/dp_gui_theextmgr.cxx
index 6d39433..46bccc9 100644
--- a/desktop/source/deployment/gui/dp_gui_theextmgr.cxx
+++ b/desktop/source/deployment/gui/dp_gui_theextmgr.cxx
@@ -495,9 +495,12 @@ void TheExtensionManager::notifyTermination( ::lang::EventObject const & rEvt )
void TheExtensionManager::modified( ::lang::EventObject const & /*rEvt*/ )
{
    m_bModified = true;
    getDialogHelper()->prepareChecking();
    DialogHelper *pDialogHelper = getDialogHelper();
    if (!pDialogHelper)
        return;
    pDialogHelper->prepareChecking();
    createPackageList();
    getDialogHelper()->checkEntries();
    pDialogHelper->checkEntries();
}