Fix message duplication due to a race-condition

.gitignore

@@ -2,3 +2,4 @@ easybridge
 config.json
 registration.yaml
 easybridge.db
+__pycache__

account.go

@@ -453,6 +453,9 @@ func (a *Account) eventInternal(event *Event) error {
 
 		var cache_key string
 		if event.Id != "" {
+			dbLockSlot(mx_room_id)
+			defer dbUnlockSlot(mx_room_id)
+
 			// If the event has an ID, make sure it is processed only once
 			cache_key = fmt.Sprintf("%s/event_seen/%s/%s",
 				a.Protocol, mx_room_id, event.Id)

server.go

@@ -165,6 +165,10 @@ func handleTxnEvent(e *mxlib.Event) error {
 			if acct != nil {
 				ev.Author = acct.Conn.User()
 				ev.Room = room.RoomID
+
+				dbLockSlot(e.RoomId)
+				defer dbUnlockSlot(e.RoomId)
+
 				created_ev_id, err := acct.Conn.Send(ev)
 				if err == nil && created_ev_id != "" {
 					cache_key := fmt.Sprintf("%s/event_seen/%s/%s",