Cosmetic change. The background color of the viewport was not being applied properly.

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@5037 3789f03b-4d11-0410-bbf8-ca57d06f2519
diff --git a/java/com/tigervnc/vncviewer/Viewport.java b/java/com/tigervnc/vncviewer/Viewport.java
index bc19b64..ba29e0a 100644
--- a/java/com/tigervnc/vncviewer/Viewport.java
+++ b/java/com/tigervnc/vncviewer/Viewport.java
@@ -107,7 +107,7 @@
     }
     if (!cc.fullScreen)
       setLocation(x, y);
-    setBackground(Color.BLACK);
+    getContentPane().setBackground(Color.BLACK);
   }
 
   public static Window getFullScreenWindow() {