tdf#116874: Don't sign with watermark if the checkbox is disabled

Change-Id: I354b0c3f0d6d29d91c1d7fa9678c4ce0bd7c8c1a
Reviewed-on: https://gerrit.libreoffice.org/52732Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Xisco Faulí <xiscofauli@libreoffice.org>

filter/source/pdf/impdialog.cxx

@@ -727,7 +727,8 @@ void ImpPDFTabGeneralPage::GetFilterConfigItem( ImpPDFTabDialog* paParent )
         paParent->mbExportFormFields = mpCbExportFormFields->IsChecked();
     }
 
-    paParent->maWatermarkText = mpEdWatermark->GetText();
+    if( mpCbWatermark->IsChecked() )
+        paParent->maWatermarkText = mpEdWatermark->GetText();
 
     /*
     * FIXME: the entries are only implicitly defined by the resource file. Should there