Merge pull request +10587 from c9/fix-vfs-headers-sent

the response might have already been sent

node_modules/vfs-http-adapter/restful.js

@@ -11,6 +11,11 @@ module.exports = function setup(mount, vfs, mountOptions) {
 
     var errorHandler = mountOptions.errorHandler || function (req, res, err, code) {
         console.error(err.stack || err);
+        if (res.headersSent) {
+            res.end("");
+            return;
+        }
+            
         if (code) res.statusCode = code;
         else if (typeof err.code == "number") res.statusCode = err.code;
         else if (err.code === "EBADREQUEST") res.statusCode = 400;