Fixes issue 3524: Catch config option not found in prefs dialog and report to user nicely.

Change-Id: Id98f89e0c3fdf5931094478ec401fa9050902ce3
Reviewed-on: http://gerrit.dmdirc.com/505
Automatic-Compile: Shane Mc Cormack <shane@dmdirc.com>
Reviewed-by: Shane Mc Cormack <shane@dmdirc.com>

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

 import net.miginfocom.layout.ComponentWrapper;
 import net.miginfocom.layout.LayoutCallback;
 
-import net.miginfocom.layout.PlatformDefaults;
 import net.miginfocom.swing.MigLayout;
 
 /**
      * serialized objects being unserialized with the new class).
      */
     private static final long serialVersionUID = -3268284364607758509L;
-    /** Panel gap. */
-    private final int padding = (int) PlatformDefaults.getUnitValueX("related").
-            getValue();
-    /** Panel left padding. */
-    private final int leftPadding = (int) PlatformDefaults.getPanelInsets(1).
-            getValue();
-    /** Panel right padding. */
-    private final int rightPadding = (int) PlatformDefaults.getPanelInsets(3).
-            getValue();
     /** Active preferences category. */
     private PreferencesCategory category;
     /** Parent window. */
     private Map<PreferencesCategory, JPanel> panels;
     /** Category loading swing worker. */
     private SwingWorker worker;
-    /** Waiting. */
-    private boolean waiting;
 
     /**
      * Instantiates a new category panel.
      * 
      * @param b
      */
-    public void setWaiting(boolean b) {
-        waiting = b;
+    public void setWaiting(final boolean b) {
         scrollPane.setViewportView(waitingCategory);
     }
+
+    /**
+     * Displays an error panel to the end user.
+     *
+     * @param message Message to display
+     */
+    public void setError(final String message) {
+        final JPanel panel = new JPanel(new MigLayout("fillx"));
+        panel.add(new TextLabel("An error has occurred loading the " +
+                "preferences dialog, an error has been raised: "), "wrap");
+        panel.add(new TextLabel(message));
+        scrollPane.setViewportView(panel);
+    }
 }

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

             @Override
             protected PreferencesManager doInBackground() throws Exception {
                 mainPanel.setWaiting(true);
-                return new PreferencesManager();
+                PreferencesManager prefsManager = null;
+                try {
+                    prefsManager = new PreferencesManager();
+                } catch (IllegalArgumentException ex) {
+                    mainPanel.setError(ex.getMessage());
+                    Logger.appError(ErrorLevel.HIGH, "Unable to load the" +
+                            "preferences dialog.", ex);
+                }
+                return prefsManager;
             }
 
             /** {@inheritDoc} */
             protected void done() {
                 if (!isCancelled()) {
                     try {
-                        setPrefsManager(get());
+                        final PreferencesManager prefsManager = get();
+                        if (prefsManager != null) {
+                            setPrefsManager(prefsManager);
+                        }
                     } catch (InterruptedException ex) {
                         //Ignore
                     } catch (ExecutionException ex) {