items with too many statements fail

[stuppie]

In Nuria's ngly1-graph, two items have 2722 and 1402 statements (MAZ (Q10572), NTRK1 (Q11027)), and fail to be written, with no error message. I don't know if there is a hard limit or its dependent on data size, as there are a couple other items that have over 1000 statements.
There is an item with 1479 statements that works fine, so it must be the total size of the item as JSON.
Maybe we can increase the size, but I'm guessing this has something to do with the actual mariadb setup (i.e. max string length a mysql table can hold)...