before_mint
Extendable function that allows the developer to add more functionality to the mint function, before the mint happens.
This allows, for example, to check that any given condition is present before minting is allowed.
If this function throws an exception, the asset will not be minted.
Throws if any extension of this function throws.
Parameters
account
the account that is going to receive the newly minted tokens
asset
the asset that is going to be minted
amount
the amount of tokens that is going to be minted