Fix wrong CURLINFO_CONTENT_LENGTH_DOWNLOAD result with redirect.

when the target file redirected to a result url which has no content-length, call getinfo for CURLINFO_CONTENT_LENGTH_DOWNLOAD will get the previous 302 page's body content-length, this commit fixed it.

test link: http://mp3.live.tv-radio.com/francemusique/all/francemusiquehautdebit.mp3