Extend to EoF when size32 is 0

[ptpt]

See the spec: https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap1/qtff1.html#//apple_ref/doc/uid/TP40000939-CH203-BBCGDDDF

0, which is allowed only for a top-level atom, designates the last atom in the file and indicates that the atom extends to the end of the file.

I don't see it's handled.