after_burn
Extendable function that allows the developer to add more functionality to the burn function, after the burn happens.
This allows, for example, to check that any given condition is present after the tokens have been burned.
If this function throws an exception, the asset will not be burned.
Throws if any extension of this function throws.
Parameters
account
the account that has lost the burned tokens
asset
the asset that has been burned
amount
the amount of tokens that have been burned