lok: handle missing callback.

Change-Id: I13a200c9c9d8b0a8fde6dd15a71fe1a665d04e8d
Reviewed-on: https://gerrit.libreoffice.org/71432
Tested-by: Jenkins
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>

libreofficekit/source/gtk/lokdocview.cxx

@@ -1449,6 +1449,8 @@ callback (gpointer pData)
     case LOK_CALLBACK_INVALIDATE_HEADER:
         g_signal_emit(pCallback->m_pDocView, doc_view_signals[INVALIDATE_HEADER], 0, pCallback->m_aPayload.c_str());
         break;
+    case LOK_CALLBACK_CONTEXT_CHANGED:
+        break; // TODO
     default:
         g_assert(false);
         break;