avformat/isom: free extradata on failure to read it

Fixes use of uninitialized memory
Fixes: msan_uninit-mem_7f607d80f661_6965_mov00003.mqv
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/isom.c

@@ -460,8 +460,11 @@ int ff_mp4_read_dec_config_descr(AVFormatContext *fc, AVStream *st, AVIOContext
         av_free(st->codec->extradata);
         if (ff_alloc_extradata(st->codec, len))
             return AVERROR(ENOMEM);
-        if ((ret = avio_read(pb, st->codec->extradata, len)) != len)
+        if ((ret = avio_read(pb, st->codec->extradata, len)) != len) {
+            av_freep(&st->codec->extradata);
+            st->codec->extradata_size = 0;
             return ret < 0 ? ret : AVERROR_INVALIDDATA;
+        }
         if (st->codec->codec_id == AV_CODEC_ID_AAC) {
             MPEG4AudioConfig cfg = {0};
             avpriv_mpeg4audio_get_config(&cfg, st->codec->extradata,