Compute index/position in Merkle tree correctly

[mitsuaki-u]

Expected behavior

For merkle tree index we unset the most significant bit of an encoded index in idxs in order to get the position in the tree. To do this we must ensure that there are at least two bits, i.e. the value must be larger than 1.

Actual behavior

idx[0] was checked for equality to 0

• Related LIP PR Compute index/position in Merkle tree correctly lips#445

Steps to reproduce

Check recover message logic verify hook

Which version(s) does this affect? (Environment, OS, etc...)

6.0.0