Fix null pointer issue. Thanks DRC, that was driving me nuts.

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4707 3789f03b-4d11-0410-bbf8-ca57d06f2519
diff --git a/java/src/com/tigervnc/vncviewer/UserPrefs.java b/java/src/com/tigervnc/vncviewer/UserPrefs.java
index b370221..f72ed5a 100644
--- a/java/src/com/tigervnc/vncviewer/UserPrefs.java
+++ b/java/src/com/tigervnc/vncviewer/UserPrefs.java
@@ -160,7 +160,7 @@
   final public static String getFileSeperator() {
     String seperator = null;
 		try {
-			seperator = System.getProperties().get("file.separator").toString();
+			seperator = (String)System.getProperties().get("file.separator");
 		} catch(java.security.AccessControlException e) {
 			System.out.println("Cannot access file.separator system property");
 		}