Enhancement of behavior about malformed MP4 files

[sunfish-shogi]

I found malformed MP4 file which was output by FFmpeg 3.0.2. go-mp4 returns EOF error at avcC box in the file.

Bento4 says the avcC box is empty (0 bytes).

A similar case was reported at: https://github.com/google/ExoPlayer/issues/6434

go-mp4's mp4tool-dump command will interrupt for all parse errors. However, sometimes we want to see informations followed error point.