Fixes issue 2275: Rendering issue with long categories in prefs dialog

Change-Id: Ie6a0b0b024627752c63d73ee72a75bb0b76a483c
Reviewed-on: http://gerrit.dmdirc.com/775
Reviewed-by: Chris Smith <chris@dmdirc.com>
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>

src/com/dmdirc/addons/ui_swing/dialogs/prefs/CategoryPanel.java

                 /** {@inheritDoc} */
                 @Override
                 public void run() {
-                    scrollPane.setViewportView(panels.get(category));
+                    final JPanel panel = panels.get(category);
+                    scrollPane.setViewportView(panel);
+                    //Hack around mig bug
+                    panel.invalidate();
+                    panel.validate();
                     if (category == null) {
                         title.setText("Preferences");
                     } else {