SPIGOT-2134: Use the correct listener in CommandExecute

nms-patches/CommandExecute.patch

@@ -41,7 +41,7 @@
 +                    } else if (listener instanceof CommandBlockListenerAbstract) {
 +                        sender = ((CommandBlockListenerAbstract) listener).sender;
 +                    } else if (listener instanceof ProxyListener) {
-+                        listener = ((ProxyListener) icommandlistener).base; // Search deeper
++                        listener = ((ProxyListener) listener).base; // Search deeper
 +                    } else if (VanillaCommandWrapper.lastSender != null) {
 +                        sender = VanillaCommandWrapper.lastSender;
 +                    } else if (listener.f() != null) {