Fix message duplicates on history load

src/main/java/fr/insa/clavardator/chat/ChatHistory.java

@@ -87,7 +87,13 @@ public class ChatHistory {
 	 * @param message The message to add
 	 */
 	public void addMessage(Message message, ErrorCallback errorCallback) {
-		db.addMessage(message, () -> Platform.runLater(() -> history.add(message)), errorCallback);
+		db.addMessage(message, () -> {
+			// Add message to active history only if we already fetched it from db
+			// This prevents duplicates when loading the db
+			if (historyLoaded) {
+				Platform.runLater(() -> history.add(message));
+			}
+		}, errorCallback);
 	}
 
 	public interface HistoryLoadedCallback {