A memory leak in ffmpeg

[MoonLight-SteinsGate]

Summary of the bug: A memory leak in function av_malloc of libavutil/mem.c:87
How to reproduce:

% ffmpeg -i PoC
ffmpeg version is ffmpeg-4.1.3
built on Ubuntu 16.04.

I have found the bug by fuzzing. I compile ffmpeg-4.1.3 to x86-64 version with address sanitizer in Ubuntu-16.04 and print the debug information as:

ffmpeg version 4.1.3 Copyright (c) 2000-2019 the FFmpeg developers

built with gcc 7 (Ubuntu 7.5.0-3ubuntu1~18.04)
configuration: --disable-stripping --prefix=/home/ubuntu/yuetai/asan_programs/ffmpeg-4.1.3/ffmpeg-install/
libavutil 56. 22.100 / 56. 22.100
libavcodec 58. 35.100 / 58. 35.100
libavformat 58. 20.100 / 58. 20.100
libavdevice 58. 5.100 / 58. 5.100
libavfilter 7. 40.101 / 7. 40.101
libswscale 5. 3.100 / 5. 3.100
libswresample 3. 3.100 / 3. 3.100

[dv @ 0x61b000000080] Format dv detected only with low score of 25, misdetection possible!
./crashes/avconv/seeds/queue/id:088235,src:077720,op:havoc,rep:64: Input/output error

=================================================================
==28203==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 33192 byte(s) in 1 object(s) allocated from:

#0 0x7fc545a3c790 in posix_memalign (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xdf790)
#1 0x555a0a559cdc in av_malloc libavutil/mem.c:87

SUMMARY: AddressSanitizer: 33192 byte(s) leaked in 1 allocation(s).

[MoonLight-SteinsGate]

PoC

[mkver]

1. Only git master is supported on this bugtracker, not an older release.
2. That bug is already fixed by 72704cbff4257466662729fc20e3f0ab85aa8c9e (fixing #8230 of which this were a duplicate if #8230 were not already fixed), but only 4.2 and above contain the fix.