Add IsStateEvent utility method for checking if EventStateKeyNID is 0

src/github.com/matrix-org/dendrite/roomserver/input/state.go

@@ -124,7 +124,7 @@ func calculateAndStoreStateMany(db RoomEventDatabase, roomNID types.RoomNID, pre
 			}
 			fullState = append(fullState, entries...)
 		}
-		if prevState.EventStateKeyNID != 0 {
+		if prevState.IsStateEvent() {
 			// If the prev event was a state event then add an entry for the event itself
 			// so that we get the state after the event rather than the state before.
 			fullState = append(fullState, prevState.StateEntry)

src/github.com/matrix-org/dendrite/roomserver/types/types.go

@@ -74,6 +74,11 @@ type StateAtEvent struct {
 	StateEntry
 }
 
+// IsStateEvent returns whether the event the state is at is a state event.
+func (s StateAtEvent) IsStateEvent() bool {
+	return s.EventStateKeyNID != 0
+}
+
 // An Event is a gomatrixserverlib.Event with the numeric event ID attached.
 // It is when performing bulk event lookup in the database.
 type Event struct {