Avoid crash in links when references are disabled

lib/rules_inline/links.js

@@ -97,6 +97,7 @@ module.exports = function links(state, silent) {
     //
     // Link reference
     //
+    if (typeof state.env.references === 'undefined') { return false; }
 
     // do not allow nested reference links
     if (state.linkLevel > 0) { return false; }