War and neutrality — War in general — Effects of outbreak of war — On private contracts — Pre-war contract with enemy company regarding retransfer of trade marks and goodwill relating to a business — Effect of war on such contract — Whether contract abrogated — Rights of the enemy company under the contract — Whether vesting in the Custodian of Enemy Property — Effect of the vesting on the right of action of the enemy company — The law of Southern Rhodesia