avformat/hlsenc: write temp file for append single file by encryption mode

avformat/hlsenc: write temp file for append single file by encryption mode

fix ticket: 8783
Because in single file by encryption mode, it cannot get the last one
block of the file, it need ff_format_io_close for get full file size,
then hlsenc can get the total size of the encryption content,
so write the content into temp file first, and get the temp file content
append the temp file content into append to single file, then hlsenc can
get the correct file/content size and offset.

Signed-off-by: Steven Liu <liuqi05@kuaishou.com>