fix: Don't fail open when a PDU doesn't have a short state hash

src/service/rooms/state_accessor/server_can.rs

@@ -1,4 +1,4 @@
-use conduwuit::{implement, utils::stream::ReadyExt};
+use conduwuit::{implement, utils::stream::ReadyExt, warn};
 use futures::StreamExt;
 use ruma::{
 	EventId, RoomId, ServerName,
@@ -19,7 +19,12 @@ pub async fn server_can_see_event(
 	event_id: &EventId,
 ) -> bool {
 	let Ok(shortstatehash) = self.pdu_shortstatehash(event_id).await else {
-		return true;
+		warn!(
+			"Unable to visibility check event {} in room {} for server {}: shortstatehash not \
+			 found",
+			event_id, room_id, origin
+		);
+		return false;
 	};
 
 	let history_visibility = self