If a written contract is altered intentionally and in a material part thereof by a person claiming a benefit under it with intent to defraud the other party, the alteration voids the whole contract, at the option of the other party. If the alteration is unintentional or by mistake or in an immaterial matter or not with intent to defraud and if the contract as originally executed can be discovered and is still capable of execution, it shall be enforced by the court. If the alteration is made by a stranger and not at the instance or by collusion of a party or privy and if the original words can be restored, the contract shall be enforced.