limit atom size to what is left, assuming container atom has correct size..
cricket4.3g2 has incorrect moov atom size which indicates that file size should be
2 bytes bigger than it is and quicktime reads it correctly though.


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@10836 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b