Harden inclusion proof verification

[ahtotruu]

Make sure the defect corrected in the Go implementation in unicitynetwork/aggregator-go#83 does not exist (or gets fixed) in Java SDK.

[b3y0urs3lf]

Checked on go aggregator commit 4052d57dad5dde14493ec023394dd991216eed01 and Java SDK commit 7980e68 .

Now if I would modify public void testShouldVerifyInclusionProof() , so that if:

1. SparseMerkleTreePath would contain negative value in the middle like new SparseMerkleTreePathStep( BigInteger.valueOf(-1), HexConverter.decode( "66507538ce0fae31018cfc7b01841b5308e7e44306445710acee947ec4a4b2cd" ) ), , then SDK would throw error "path should be non negative"

2. SparseMerkleTreePath would contain 0 value in the middle like new SparseMerkleTreePathStep( BigInteger.valueOf(0), HexConverter.decode( "66507538ce0fae31018cfc7b01841b5308e7e44306445710acee947ec4a4b2cd" ) ), , then SDK would throw error "Expected :
   MerkleTreePathVerificationResult{pathValid=true, pathIncluded=true}
   Actual :MerkleTreePathVerificationResult{pathValid=false, pathIncluded=false} which is according to developer is now expected. Also according to developer he will extend current test so it would have mentioned test cases.

Moving task to done.