One who hires part of a room for a dwelling is entitled to the whole of the room, notwithstanding any agreement to the contrary; and if a landlord lets a room as a dwelling for more than one family, the person to whom he first lets any part of it is entitled to the possession of the whole room for the term agreed upon, and every tenant in the building, under the same landlord, is relieved from all obligation to pay rent to him while such double letting of any room continues.