This fixes a null pointer exception in a config that loads permission.so but does not set its db_url.
To repro, create a config with loadmodule "permissions.so" but NOT modparam("permissions", "db_url", "foo"), and then run "kamctl trusted reload". Kamailio will crash without this patch. With this patch, kamctl will return with "Reload failed" and a message will be printed in kamailio logs.