Models::getNextId is unreliable

[jameswilddev]

The value returned by show table status is often cached (see https://stackoverflow.com/questions/52705477/mysql-show-table-status-auto-increment-is-not-correct), so it is possible to get an out-of-date value from this function.

[jameswilddev]

(conceptually I feel the function is a bit flawed, as this is generally used to fill secondary columns with values generated from the ID, e.g. reference numbers, but there's nothing to guarantee another transaction didn't take the proposed ID AFAICT)