Instead of NPEing when we reset _oin at a bad time, let's throw an exception we can better handle and reduce some log spew.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@6150 542714f4-19e9-0310-aa3c-eee0fc999fb1

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

@@ -486,6 +486,12 @@ public class BlockingCommunicator extends Communicator
             // noop!
         }
 
+        if (_oin == null) {
+            // Our object input stream was taken away from us before we could do anything with the
+            //  frame, this is equivalent to being interrupted mid-frame, so indicate that.
+            throw new InterruptedIOException();
+        }
+
         try {
             int size = _fin.available();
             DownstreamMessage msg = (DownstreamMessage)_oin.readObject();