crash on linux when selecting columns after inserting large blobs

[PThorpe92]

In the process of running some tests for batch processing of writes in #557, I did something like:

INSERT INTO t (t1, t2) VALUES (zeroblob(4096*4096), zeroblob(4096*1024));

As usual, I would open the .db file in sqlite3, and make sure I could run .schema, and a select * from t;, to ensure it did not corrupt the db file with partial writes. While sqlite3 had no issue with this, limbo crashed on select * from t and I was worried at first it was an issue with the changes I had made to the linux IO module.

I re-built limbo from main and attempted again and this problem persists. I created a new .db file with sqlite3 with similar blob inserts, again on the main branch with the same outcome.

I'll be working on this, as it's adjacent to the other io issue.

EDIT: *confirmed this isn't a problem with in-memory IO. I'll see if I can get someone to try on a mac. confirmed not a problem on mac as well.