Chen v. Holder, 658 F.3d 246 (2d Cir. Sept. 23, 2011) (claim that respondent's husband was unavailable to testify in support of his wife's asylum claim due to fear of apprehension does not establish that husband was not available to testify to corroborate asylum claim; in this instance, husband's testimony, if helpful in allow spouse to obtain asylee status, would also have allowed the husband to obtain status as a derivative).