Injunction to perform negative agreement.Notwithstanding anything contained in clause e of section 41, where a contract comprises an affirmative agreement to do a certain act, coupled with a negative agreement, express or implied, not to do a certain act, the circumstances that the court is unable to compel specific performance of the affirmative agreement shall not preclude it from granting an injunction to perform the negative agreement Provided that the plaintiff has not failed to perform the contract so far as it is binding on him.