Fixed handling of NULL entries in osg::Geometry TexCoordArrayList and VertexAttribArrayList.

git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14715 16af8721-9629-0410-8352-f15c8da7e697

src/osgDB/OutputStream.cpp

@@ -577,7 +577,11 @@ void OutputStream::writeImage( const osg::Image* img )
 
 void OutputStream::writeObject( const osg::Object* obj )
 {
-    if ( !obj ) return;
+    if ( !obj )
+    {
+        *this << std::string("NULL") << std::endl;  // Write NULL token.
+        return;
+    }
 
     std::string name = obj->libraryName();
     name += std::string("::") + obj->className();