we encode the thumbnail directly after the header, but we need/want? to encode it with r13c3 much later (at the very end, after MEASUREMENT). and then patchup the address/crc in the  header.
currently we do write the wrong header.thumbnail_address, mismatching the actual thumbnail start (fixed)

r13b1-r14: directly after header (88)
r13c3-r2000: after MEASUREMENT or AUXHEADER

as from the spec r13-r2000:
* HEADER
  * FILE HEADER
  * HEADER VARIABLES
* CLASS
* MEASUREMENT (R13 only, optional)
* PADDING (R13C3 and later)
* THUMBNAIL (Pre-R13C3)
* OBJECTS
* HANDLES
* OBJECT FREE SPACE (optional)
* MEASUREMENT (R14-R2000, optional)
* AuxHEADER (=SECOND HEADER, optional for R13C3 and later)
*  THUMBNAIL (R13C3 and later)

encode thumbnail_address r13c3
This is a GitHub Issue
repo:libredwg
owner:LibreDWG
Title : encode thumbnail_address r13c3
Issue date:

--- start body ---
we encode the thumbnail directly after the header, but we need/want? to encode it with r13c3 much later (at the very end, after MEASUREMENT). and then patchup the address/crc in the  header.
currently we do write the wrong header.thumbnail_address, mismatching the actual thumbnail start (fixed)

r13b1-r14: directly after header (88)
r13c3-r2000: after MEASUREMENT or AUXHEADER

as from the spec r13-r2000:
* HEADER
  * FILE HEADER
  * HEADER VARIABLES
* CLASS
* MEASUREMENT (R13 only, optional)
* PADDING (R13C3 and later)
* THUMBNAIL (Pre-R13C3)
* OBJECTS
* HANDLES
* OBJECT FREE SPACE (optional)
* MEASUREMENT (R14-R2000, optional)
* AuxHEADER (=SECOND HEADER, optional for R13C3 and later)
*  THUMBNAIL (R13C3 and later)

--- end body ---
