Make sure default exception handler is used unless overriden

Author: michaelklishin

src/com/rabbitmq/client/impl/AMQConnection.java

@@ -111,7 +111,7 @@ public static final Map<String, Object> defaultClientProperties() {
     private volatile boolean _running = false;
 
     /** Handler for (uncaught) exceptions that crop up in the {@link MainLoop}. */
-    private ExceptionHandler _exceptionHandler;
+    private ExceptionHandler _exceptionHandler = new DefaultExceptionHandler();
 
     /** Object used for blocking main application thread when doing all the necessary
      * connection shutdown operations