fixed issue 529

http://code.google.com/p/jmonkeyengine/issues/detail?id=529&q=label%3AProduct-jME3&colspec=ID%20Type%20Status%20Component%20Priority%20Difficulty%20Product%20Milestone%20Owner%20Summary

git-svn-id: https://jmonkeyengine.googlecode.com/svn/trunk@10038 75d07b2b-3a1a-0410-a2c5-0572b91ccdca

engine/src/desktop/com/jme3/system/JmeDesktopSystem.java

@@ -103,7 +103,10 @@ public class JmeDesktopSystem extends JmeSystemDelegate {
 
         final AppSettings settings = new AppSettings(false);
         settings.copyFrom(sourceSettings);
-        String iconPath = sourceSettings.getSettingsDialogImage();
+        String iconPath = sourceSettings.getSettingsDialogImage();        
+        if(iconPath == null){
+            iconPath = "";
+        }
         final URL iconUrl = JmeSystem.class.getResource(iconPath.startsWith("/") ? iconPath : "/" + iconPath);
         if (iconUrl == null) {
             throw new AssetNotFoundException(sourceSettings.getSettingsDialogImage());