catch a panic in merkle proof verification

[dan]

Currently, there is a panic in winterfell's crypto crate when verifying a Merkle proof, see #200
The lib assumes that the prover honestly informs the verifier about the total amount of leaves in the tree as well as the leaf indices being proved.

The same type of assumption and panics are present in other merkle libs:
antouhou/rs-merkle#20
https://github.com/rozbb/ct-merkle/blob/e29d123e1b45b0e652e5ee5e4c288ff3792652e5/src/batch_inclusion.rs#L404

Until this issue is fixed upstream, we should wrap the verification in panic::catch_unwind.

[dan]

oops, opened this issue under the wrong project, sry.