Affiliations other than admin and owner cannot invite to members_only rooms

This is explained in the paragraph:
 If the room is members-only, the service MAY also add the invitee to the
 member list. (Note: Invitation privileges in members-only rooms SHOULD be
 restricted to room admins; if a member without privileges to edit the
 member list attempts to invite another user, the service SHOULD return
 a <forbidden/> error to the occupant; for details, see the Modifying the
 Member List section of this document.)
https://xmpp.org/extensions/xep-0045.html#invite-mediated

src/mod_muc_room.erl

@@ -4217,7 +4217,8 @@ send_voice_request(From, Lang, StateData) ->
 			      ok | {error, stanza_error()}.
 check_invitation(From, Invitations, Lang, StateData) ->
     FAffiliation = get_affiliation(From, StateData),
-    CanInvite = (StateData#state.config)#config.allow_user_invites orelse
+    CanInvite = ((StateData#state.config)#config.allow_user_invites
+	        and not (StateData#state.config)#config.members_only) orelse
 	        FAffiliation == admin orelse FAffiliation == owner,
     case CanInvite of
 	true ->