Only using getErrorStream() for status >= 400

TypedInput in() should only use getErrorStream() when status >= 400 because getErrorStream() returns null unless responseCode >= 400 (see: http://hg.openjdk.java.net/jdk6/jdk6-gate/jdk/file/tip/src/share/classes/sun/net/www/protocol/http/HttpURLConnection.java)