Don't process chat if the mcMMOPlayer is null.

The player should ALWAYS be online when chatting, but depending on
external plugins and applications, this is not always properly
implemented. Fixes #1578

src/main/java/com/gmail/nossr50/listeners/PlayerListener.java

@@ -619,6 +619,13 @@ public class PlayerListener implements Listener {
         }
 
         McMMOPlayer mcMMOPlayer = UserManager.getPlayer(player, true);
+        
+        if (mcMMOPlayer == null) {
+            mcMMO.p.debug(player.getName() + "is chatting, but is currently not logged in to the server.");
+            mcMMO.p.debug("Party & Admin chat will not work properly for this player.");
+            return;
+        }
+
         ChatManager chatManager = null;
 
         if (mcMMOPlayer.getPartyChatMode()) {