Fix undefined var exception

Summary: This check to see if `require` exists was bad as it throws an error for an
undefined reference in case it doesn't exist.
Closes https://github.com/facebook/react-native/pull/3845

Reviewed By: svcscm

Differential Revision: D2613368

Pulled By: martinbigio

fb-gh-sync-id: 7b1d0f38e4af9bce81356a613d6105f2c00c7ed7

local-cli/server/util/debuggerWorker.js

@@ -21,7 +21,7 @@ var messageHandlers = {
   'executeJSCall': function(message, sendReply) {
     var returnValue = [[], [], [], [], []];
     try {
-      if (require) {
+      if (typeof require === 'function') {
         returnValue = require(message.moduleName)[message.moduleMethod].apply(null, message.arguments);
       }
     } finally {