internal: check flush err (#2632)
internal: check flush err (#2632)


stanley-cheung/grpc-go,thinkerou/grpc-go,grpc/grpc-go,menghanl/grpc-go,thinkerou/grpc-go,grpc/grpc-go,dfawley/grpc-go,menghanl/grpc-go,stanley-cheung/grpc-go,dfawley/grpc-go