use blocksize for msiDataObjRead loop

[trel]

instead of maxsize, all at once

[korydraughn]

What does this mean exactly?

msiDataObjRead requires you to tell it how many bytes to read.

[trel]

The current implementation of 'gether' just grabs all the data in a data object holding a schema in a single read. That could be 'too much', and this is to investigate looping through smaller reads to get the complete contents of the data object.

These files are relatively small (just JSON-Schema documents)... so this effort may prove to be overkill / not worth it.