By Samia NakhoulDUBAI, April 1 (Reuters) - If President Donald Trump ends the war with Iran without a deal, he risks leaving Tehran with a stranglehold over Middle East energy supplies and Gulf Arab oil and gas producers grappling with the fallout of a conflict they did not start or shape.Instead of crushing Iran's theocratic rulers, it could leave them stronger, emboldened by surviving weeks of U.S.-Israeli attacks, firing on Arab Gulf states and rattling global energy markets by effectively s...