fix: force conversion of withdrawal code

[gballet]

This is a tentative fix that is probably unnecessary but that I am keeping around in case my analysis is wrong and the fix is indeed needed.

During the overlay transition, withdrawals to unconverted addresses will cause the account to be loaded, but not its code/data. if that is the case, then we have this strange situation where the code is not in the tree but a non-empty code hash refers to it.

this shouldn't be a problem since, as said, fullnodes store the code out of the tree, and so the code will be found as soon as the code hash can be read. nonetheless, the account will be partially translated until the account is converted and so the node commitment will reflect that. this can be surprising to stateless clients, although they should not function during the conversion anyway.