Fixes #1816 - HttpClientTest.testClientCannotValidateServerCertificate() hangs with JDK 9.

Now upgrading the connection also in cased of filled=-1, so that the
new nested connection attempts to read/write and will see a failure
(although not the SslHandshakeException).

jetty-io/src/main/java/org/eclipse/jetty/io/NegotiatingClientConnection.java

@@ -80,13 +80,17 @@ public abstract class NegotiatingClientConnection extends AbstractConnection
         while (true)
         {
             int filled = fill();
-            if (filled == 0 && !completed)
-                fillInterested();
-            if (filled <= 0 || completed)
+            if (completed || filled < 0)
+            {
+                replaceConnection();
                 break;
+            }
+            if (filled == 0)
+            {
+                fillInterested();
+                break;
+            }
         }
-        if (completed)
-            replaceConnection();
     }
 
     private int fill()