fix app-level error delegation, always delgate

lib/context.js

@@ -562,10 +562,12 @@ module.exports = {
    */
 
   onerror: function(err){
+    this.app.onerror(err);
+    
     // nothing we can do here other
     // than delegate to the app-level
     // handler and log.
-    if (this.headerSent) return this.app.onerror(err);
+    if (this.headerSent) return;
 
     // err.status support
     if (err.status) {