1.4.3. db_does_uri_exist()
Check if username in the request URI belongs to an existing user.
Matching is done against the URI table (if use_uri_table is set) or the subscriber table.
This function can be used from REQUEST_ROUTE.
Example 1.13. db_does_uri_exist usage
...
if (db_does_uri_exist()) {
...
};
...
