add new test case not covered by RLP tests
add new test case not covered by RLP tests

We discovered that our implementation of RLP encoding decodes some RLP binaries incorrectly after recent PR (https://github.com/mana-ethereum/ex_rlp/pull/17) but it passes all RLP test cases. 

This PR adds a new test case which is not covered by existing RLP tests
ethereum/tests,ethereum/tests,ethereum/tests