Prevent the users from attaching an external db file which they may not
have ownership of.
The current authorizer method is hooked in only when the LNAVSECURE
variable is set. This is done deliberately, since the method will be
called on every sqlite query and I did not want to incur a performance
hit.
If the scope of this authorizer increases, we should consider passing in
the lnav_data as pUserData and do the checks inside the authorizer
itself.