cosocket: added a test case for extremely small buffers when calling sock:receiveuntil.
cosocket: added a test case for extremely small buffers when calling sock:receiveuntil.

yeahdongcn/SEnginx,yeahdongcn/SEnginx,yeahdongcn/SEnginx,yeahdongcn/SEnginx,yeahdongcn/SEnginx,yeahdongcn/SEnginx,yeahdongcn/SEnginx