A Chinese critic of his country’s ruling Communist Party had already escaped to Thailand and Vietnam and tried swimming to Taiwan — only to be sent back to mainland China each time. He was jailed, prohibited from working and barred from leaving, despite international calls to let him seek asylum elsewhere. Now the dissident, Dong Guangping, 68, is in custody in South Korea after escaping China by sea, two of his friends and his lawyer told The New York Times. They said he arrived in a rubber boat late Monday.…