make 'Navigate By' control avaliable in read only mode

Change-Id: I02926aa962c045081dcf61bfc7a8d2cf522d6e92
Reviewed-on: https://gerrit.libreoffice.org/47011Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>
Tested-by: Katarina Behrens <Katarina.Behrens@cib.de>

sw/sdi/swriter.sdi

@@ -7672,7 +7672,7 @@ SfxVoidItem NavElement FN_NAV_ELEMENT
 [
     AutoUpdate = TRUE,
     FastCall = FALSE,
-    ReadOnlyDoc = FALSE,
+    ReadOnlyDoc = TRUE,
     Toggle = FALSE,
     Container = FALSE,
     RecordAbsolute = FALSE,