Validates the topic in the topic bar on open to cope with change in bahaviour of core vs parser topic listener

Change-Id: Ib29f9c1bd96ee210d133f47858684dcf391797b0
Reviewed-on: http://gerrit.dmdirc.com/669
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>
Reviewed-by: Shane Mc Cormack <shane@dmdirc.com>

src/com/dmdirc/addons/ui_swing/components/TopicBar.java

@@ -204,6 +204,7 @@ public class TopicBar extends JComponent implements ActionListener,
         topicText.setEditable(false);
         topicCancel.setVisible(false);
         setColours();
+        validateTopic();
     }
 
     /** {@inheritDoc} */