mov: reset dref_count on realloc to keep values consistent.

This fixes a potential crash.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
static AVIndexEntry *mov_find_next_sample(AVFormatContext *s, AVStream **st)
{
    AVIndexEntry *sample = NULL;
    int64_t best_dts = INT64_MAX;
    int i;
    for (i = 0; i < s->nb_streams; i++) {
        AVStream *avst = s->streams[i];
        MOVStreamContext *msc = avst->priv_data;
        if (msc->pb && msc->current_sample < avst->nb_index_entries) {
            AVIndexEntry *current_sample = &avst->index_entries[msc->current_sample];
            int64_t dts = av_rescale(current_sample->timestamp, AV_TIME_BASE, msc->time_scale);
            av_dlog(s, "stream %d, sample %d, dts %"PRId64"\n", i, msc->current_sample, dts);
            if (!sample || (!s->pb->seekable && current_sample->pos < sample->pos) ||
                (s->pb->seekable &&
                 ((msc->pb != s->pb && dts < best_dts) || (msc->pb == s->pb &&
                 ((FFABS(best_dts - dts) <= AV_TIME_BASE && current_sample->pos < sample->pos) ||
                  (FFABS(best_dts - dts) > AV_TIME_BASE && dts < best_dts)))))) {
                sample = current_sample;
                best_dts = dts;
                *st = avst;
            }
        }
    }
    return sample;
}

static AVIndexEntry *mov_find_next_sample(AVFormatContext *s, AVStream **st)
{
    AVIndexEntry *sample = NULL;
    int64_t best_dts = INT64_MAX;
    int i;
    for (i = 0; i < s->nb_streams; i++) {
        AVStream *avst = s->streams[i];
        MOVStreamContext *msc = avst->priv_data;
        if (msc->pb && msc->current_sample < avst->nb_index_entries) {
            AVIndexEntry *current_sample = &avst->index_entries[msc->current_sample];
            int64_t dts = av_rescale(current_sample->timestamp, AV_TIME_BASE, msc->time_scale);
            av_dlog(s, "stream %d, sample %d, dts %"PRId64"\n", i, msc->current_sample, dts);
            if (!sample || (!s->pb->seekable && current_sample->pos < sample->pos) ||
                (s->pb->seekable &&
                 ((msc->pb != s->pb && dts < best_dts) || (msc->pb == s->pb &&
                 ((FFABS(best_dts - dts) <= AV_TIME_BASE && current_sample->pos < sample->pos) ||
                  (FFABS(best_dts - dts) > AV_TIME_BASE && dts < best_dts)))))) {
                sample = current_sample;
                best_dts = dts;
                *st = avst;
            }
        }
    }
    return sample;
}
