gtktiledviewer: Handle LOK_CALLBACK_SIGNATURE_STATUS to avoid an assert.

Change-Id: Iae56708d94a229911a5d008d519120ac59069cf3
Reviewed-on: https://gerrit.libreoffice.org/63391
Tested-by: Jenkins
Reviewed-by: Jan Holesovsky <kendy@collabora.com>

libreofficekit/source/gtk/lokdocview.cxx

@@ -1029,6 +1029,11 @@ globalCallback (gpointer pData)
         reportError(pCallback->m_pDocView, pCallback->m_aPayload);
     }
     break;
+    case LOK_CALLBACK_SIGNATURE_STATUS:
+    {
+        // TODO
+    }
+    break;
     default:
         g_assert(false);
         break;