refactor(merkle): cosmetic cleanup on ProveLeafRec return

Author: mpolitzer

internal/merkle/builder.go

@@ -260,15 +260,15 @@ func (tree *Tree) ProveLeafRec(index *big.Int) (*Proof, error) {
 		}
 		proof.PushHash(rhs.RootHash)
 		proof.Pos = index
-		return proof, err
+		return proof, nil
 	} else {
 		proof, err := rhs.ProveLeafRec(innerIndex)
 		if err != nil {
 			return nil, err
 		}
 		proof.PushHash(lhs.RootHash)
 		proof.Pos = index
-		return proof, err
+		return proof, nil
 	}
 }