Stall even with --untimed with fuzzed file.

[tholin]

Running this file like mpv --no-config --untimed --vo null --ao=null:untimed random_hang.mp3 will stall for a few minutes until it eventually exit. Most of that time is spent idle with all threads parked. It's not what I expect from untimed playback.
https://www.dropbox.com/s/0k2g7am3gy2hllz/random_hang.mp3

$ time ~/repository/mpv-build_vanilla_debug/mpv/build/mpv --no-config --untimed --vo null --ao=null:untimed random_hang.mp3 
Playing: random_hang.mp3
[ffmpeg/audio] mp3: Header missing
[ffmpeg/audio] mp3: Header missing
[ffmpeg/audio] mp3: Header missing
[ffmpeg/demuxer] mp3: Estimating duration from bitrate, this may be inaccurate
 (+) Audio --aid=1 (mp3)
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
AO: [null] 44100Hz mono 1ch s16p
AO: [null] 44100Hz stereo 2ch s16p
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
A: 00:00:00 / 00:00:00 (19%)
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
A: 00:00:00 / 00:00:00 (36%)
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
A: 00:00:00 / 00:00:00 (42%)
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
A: 00:00:00 / 00:00:00 (42%)
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
[ffmpeg/audio] mp3: Header missing
Error decoding audio.
A: 00:00:00 / 00:00:00 (42%)

Exiting... (End of file)

real    3m20.371s
user    0m0.020s
sys     0m0.006s

[ghost]

Yeah, fails to decode audio, and then decides to do nothing.