fix: don't do Quest#onCompleted work twice

Can happen if a quest has multiple optional tasks where completing one
task completes the quest.

FTBTeam/FTB-Mods-Issues#1390

common/src/main/java/dev/ftb/mods/ftbquests/quest/Quest.java

@@ -542,20 +542,23 @@ public void onStarted(QuestProgressEventData<?> data) {
 
 	@Override
 	public void onCompleted(QuestProgressEventData<?> data) {
-		data.setCompleted(id);
-		ObjectCompletedEvent.QUEST.invoker().act(new ObjectCompletedEvent.QuestEvent(data.withObject(this)));
+		if (!data.getTeamData().isCompleted(this)) {
+			// it's possible this quest is already completed, if it has one or more optional tasks
+			data.setCompleted(id);
+			ObjectCompletedEvent.QUEST.invoker().act(new ObjectCompletedEvent.QuestEvent(data.withObject(this)));
 
-		if (!disableToast) {
-			data.notifyPlayers(id);
-		}
+			if (!disableToast) {
+				data.notifyPlayers(id);
+			}
 
-		if (chapter.isCompletedRaw(data.getTeamData())) {
-			chapter.onCompleted(data.withObject(chapter));
-		}
+			if (chapter.isCompletedRaw(data.getTeamData())) {
+				chapter.onCompleted(data.withObject(chapter));
+			}
 
-		data.getTeamData().checkAutoCompletion(this);
+			data.getTeamData().checkAutoCompletion(this);
 
-		checkForDependantCompletion(data.getTeamData());
+			checkForDependantCompletion(data.getTeamData());
+		}
 	}
 
 	private void checkForDependantCompletion(TeamData data) {