mod_muc_rtbl: Optimize case with zero hashes On the assumption that during quiet times between torrents of spam, the hash set would be empty. There would be no point in doing the operations and hashes to check for a match in that case.

This module blocks configured queries that change server state.

E.g. to make vCard storage read-only:

``` lua
readonly_stores = {
	vcard = { "vcard-temp", "vCard" };
}
```