AuraSpell#openPositionFarm uses incorrect join type for balancer

Summary

The JoinPoolRequest uses "" for userData meaning that it will decode into 0. This is problematic because join requests of type 0 are "init" type joins and will revert for pools that are already initialized.

Vulnerability Detail

https://etherscan.io/address/0x5c6ee304399dbdb9c8ef030ab642b10820db8f56#code#F24#L49

enum JoinKind { INIT, EXACT_TOKENS_IN_FOR_BPT_OUT, TOKEN_IN_FOR_EXACT_BPT_OUT }

We see above that enum JoinKind is INIT for 0 values.

https://etherscan.io/address/0x5c6ee304399dbdb9c8ef030ab642b10820db8f56#code#F24#L290

        return _joinExactTokensInForBPTOut(balances, normalizedWeights, userData);
    } else if (kind == JoinKind.TOKEN_IN_FOR_EXACT_BPT_OUT) {
        return _joinTokenInForExactBPTOut(balances, normalizedWeights, userData);
    } else {
        _revert(Errors.UNHANDLED_JOIN_KIND);
    }

Here user data is decoded into join type and since it is "" it will decode to type 0 which will result in a revert.