Fix NPE in privacy lists when presence packet has no TO address

Related thread: http://www.jivesoftware.org/community/thread.jspa?threadID=20563&tstart=0

java.lang.NullPointerException
at org.jivesoftware.wildfire.privacy.PrivacyItem.verifyJID(PrivacyItem.java:166)
at org.jivesoftware.wildfire.privacy.PrivacyItem.matchesPacketSenderCondition(PrivacyItem.java:145)
at org.jivesoftware.wildfire.privacy.PrivacyItem.matchesCondition(PrivacyItem.java:127)
at org.jivesoftware.wildfire.privacy.PrivacyList.shouldBlockPacket(PrivacyList.java:102)
at org.jivesoftware.wildfire.ClientSession.shouldBlockPacket(ClientSession.java:732)
at org.jivesoftware.wildfire.ClientSession.process(ClientSession.java:743)
at org.jivesoftware.wildfire.handler.PresenceUpdateHandler.initSession(PresenceUpdateHandler.java:199)
at org.jivesoftware.wildfire.handler.PresenceUpdateHandler.process(PresenceUpdateHandler.java:100)
at org.jivesoftware.wildfire.handler.PresenceUpdateHandler.process(PresenceUpdateHandler.java:153)
at org.jivesoftware.wildfire.PresenceRouter.handle(PresenceRouter.java:92)
at org.jivesoftware.wildfire.PresenceRouter.route(PresenceRouter.java:61)
at org.jivesoftware.wildfire.spi.PacketRouterImpl.route(PacketRouterImpl.java:75)
at org.jivesoftware.wildfire.net.SocketReader.processPresence(SocketReader.java:296)
at org.jivesoftware.wildfire.net.ClientSocketReader.processPresence(ClientSocketReader.java:57)
at org.jivesoftware.wildfire.net.SocketReader.process(SocketReader.java:191)
at org.jivesoftware.wildfire.net.BlockingReadingMode.readStream(BlockingReadingMode.java:156)
at org.jivesoftware.wildfire.net.BlockingReadingMode.run(BlockingReadingMode.java:62)
at org.jivesoftware.wildfire.net.SocketReader.run(SocketReader.java:123)
at java.lang.Thread.run(Thread.java:595)