avformat/hls: Fix DoS due to infinite loop

Fixes: loop.m3u

The default max iteration count of 1000 is arbitrary and ideas for a better solution are welcome

Found-by: Xiaohei and Wangchu from Alibaba Security Team

Previous version reviewed-by: Steven Liu <lingjiujianke@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
static void free_rendition_list(HLSContext *c)
{
    int i;
    for (i = 0; i < c->n_renditions; i++)
        av_freep(&c->renditions[i]);
    av_freep(&c->renditions);
    c->n_renditions = 0;
}

static void free_rendition_list(HLSContext *c)
{
    int i;
    for (i = 0; i < c->n_renditions; i++)
        av_freep(&c->renditions[i]);
    av_freep(&c->renditions);
    c->n_renditions = 0;
}
