xref column truncated data SQL Error

[rbrostowiez]

###Expected behaviour
No errors in execution log of file: misc/update/nix/screen/threaded/start.sh

With a fresh install, and a single group enabled with backfill, I receive the below error message thousands of times per operation.

###Actual behaviour
SQL Error when inserting collections Error: SQLSTATE[22001]: String data, right truncated: 1406 Data too long for column 'xref' at row 1

###Steps to reproduce the behaviour
Execute: misc/update/nix/screen/threaded/start.sh

###Suggested solution:
At: nzedb/Binaries.php:941 the xref column value being set is a concatenation of current value + up to 254 characters. I have wrapped that concatenation with a substring call which will prevent column overflow to avoid the SQL Errors regarding the truncation of column data.

PR will be Submitted alongside this ticket.