Fix NPE in window status plugin.

Change-Id: I8eff130e8a21ec1623541e4033308489a4b6be04
Fixes-Issue: CLIENT-355
Reviewed-on: http://gerrit.dmdirc.com/2424
Reviewed-by: Chris Smith <chris@dmdirc.com>
Automatic-Compile: DMDirc Build Manager

src/com/dmdirc/addons/windowstatus/WindowStatusPlugin.java

@@ -205,7 +205,7 @@ public final class WindowStatusPlugin extends BasePlugin
                 final ClientInfo client = frame.getServer().getParser()
                         .getClient(frame.getHost());
                 final String realname = client.getRealname();
-                if (!realname.isEmpty()) {
+                if (realname != null && !realname.isEmpty()) {
                     textString.append(" - ");
                     textString.append(client.getRealname());
                 }