Prevent NPE when we process a pong that was destined for a different

DeltaCalculator.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@4003 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/presents/client/DeltaCalculator.java

@@ -69,6 +69,11 @@ public class DeltaCalculator
      */
     public boolean gotPong (PongResponse pong)
     {
+        if (_ping == null) {
+            // an errant pong that is likely being processed late after
+            // a new connection was opened.
+            return false;
+        }
         // don't freak out if they keep calling gotPong() after we're done
         if (_iter >= _deltas.length) {
             return true;