Fixed undeploy race condition

Fix for following error that seems to be a race condition that occasionally occurs when an application under load is undeployed - The beanContext Data has not been set:
2011-11-24 08:13:10,996 FATAL [OpenEJB.server.remote.ejb] (ejbd 13) Unknown error in container
java.lang.NullPointerException
at org.apache.openejb.core.stateless.StatelessInstanceManager.discardInstance(StatelessInstanceManager.java:259)
at org.apache.openejb.core.stateless.StatelessContainer.invoke(StatelessContainer.java:185)
at org.apache.openejb.core.stateless.StatelessContainer.invoke(StatelessContainer.java:142)
at org.apache.openejb.server.ejbd.EjbRequestHandler.doEjbObject_BUSINESS_METHOD(EjbRequestHandler.java:266)
at org.apache.openejb.server.ejbd.EjbRequestHandler.processRequest(EjbRequestHandler.java:135)
at org.apache.openejb.server.ejbd.EjbDaemon.processEjbRequest(EjbDaemon.java:234)
at org.apache.openejb.server.ejbd.EjbDaemon.service(EjbDaemon.java:164)
at org.apache.openejb.server.ejbd.EjbServer.service(EjbServer.java:71)
at org.apache.openejb.server.ejbd.KeepAliveServer$Session.service(KeepAliveServer.java:213)
at org.apache.openejb.server.ejbd.KeepAliveServer.service(KeepAliveServer.java:233)
at org.apache.openejb.server.ejbd.EjbServer.service(EjbServer.java:66)
at org.apache.openejb.server.ServicePool$2.run(ServicePool.java:91)
at org.apache.openejb.server.ServicePool$3.run(ServicePool.java:120)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)'}