Fix textpane background caching for the life of the JVM

Change-Id: I5e607e229795c0a535651d7b97a418a11695d591
Reviewed-on: http://gerrit.dmdirc.com/413
Tested-by: Gregory Holmes <greboid@dmdirc.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>
Tested-by: Chris Smith <chris@dmdirc.com>

src/com/dmdirc/addons/ui_swing/textpane/TextPaneCanvas.java

@@ -180,7 +180,7 @@ class TextPaneCanvas extends JPanel implements MouseInputListener,
             @Override
             public void run() {
                 backgroundImage = backgroundPath.isEmpty() ? null : Toolkit.
-                getDefaultToolkit().getImage(URLBuilder.buildURL(backgroundPath));
+                getDefaultToolkit().createImage(URLBuilder.buildURL(backgroundPath));
                 repaint();
             }
         });