Backport ProxyUtils clean up, close AsyncHttpClient#507

Author: Stephane Landelle

src/main/java/com/ning/http/util/ProxyUtils.java

@@ -205,6 +205,7 @@ public ProxyServer select(URI uri) {
                             case HTTP:
                                 if (!(proxy.address() instanceof InetSocketAddress)) {
                                     log.warn("Don't know how to connect to address " + proxy.address());
+                                    return null;
                                 } else {
                                     InetSocketAddress address = (InetSocketAddress) proxy.address();
                                     return new ProxyServer(Protocol.HTTP, address.getHostName(), address.getPort());