Should be pass EMPTY DOCUMENT without throwing exception

[GoogleCodeExporter]

from this code 
http://code.google.com/p/google-gson/source/browse/trunk/gson/src/main/java/com/
google/gson/stream/JsonWriter.java?r=615#416

It only check for document to end properly, but sometime we just open 
JSonWriter but later logic don't write anything so we just want to close then 
it will throw exception

Which I think is no need, it should be check or if peek() != 
JsonScope.EMPTY_DOCUMENT too, or changing JsonScope to drop EMPTY and NONEMPTY, 
just check that scope stack is empty and that's all

Original issue reported on code.google.com by thainayu on 19 Mar 2012 at 7:55