libavformat/hls: Free keys

Fixes: memleak
Fixes: 50703/clusterfuzz-testcase-minimized-ffmpeg_dem_HLS_fuzzer-6399058578636800

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegReviewed-by: Steven Liu <lingjiujianke@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/hls.c

@@ -250,6 +250,7 @@ static void free_init_section_list(struct playlist *pls)
 {
     int i;
     for (i = 0; i < pls->n_init_sections; i++) {
+        av_freep(&pls->init_sections[i]->key);
         av_freep(&pls->init_sections[i]->url);
         av_freep(&pls->init_sections[i]);
     }