Because db->conn is a void *, changing it (from a direct pointer to
a pointer to a pair of pointers) did not break compile if one place hadn't
been update.
The result was a confusing failure: sqlite3 complaining about API misuse,
since the db->conn pointer was not a valid db handle any more.
This is one case where avoiding a void * is hard: we might not even
have the postgresql types, since it might not be installed. But a union
would have been superior here.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>