Allow NullPointer to be passed to sqlite3_set_authorizer

[louwers]

Only a single authorizer can be in place on a database connection at a time. Each call to sqlite3_set_authorizer overrides the previous call. Disable the authorizer by installing a NULL callback. The authorizer is disabled by default.

https://www.sqlite.org/c3ref/set_authorizer.html

[tomayac]

Thanks, this will be part of the next build.