(0x00000001)
The TCODE_COMMENTBLOCK is the first chunk in the file, starts 32 bytes into
the file, and contains text information terminated with a ^m_z. This ^m_z and
contents of this chunk were expanded in February 2000. Files written with
code released earlier than this will not have the ^m_z.
(0x00007FFF)
The TCODE_ENDOFFILE is the last chunk in the file and the first 4 bytes
of information in this chunk is an integer that contains the file length.
This chunk was added in February 2000 and files written with code released
earlier than this will not have this termination block.
(0x00007FFE)
this typecode is returned when a rogue eof marker is found
Some v1 3dm file writers put these markers in a "goo".
Simply skip these chunks and continue.