Empty-string anim queues are now allowed

Source/Integration/AnimQueue.cpp

@@ -420,8 +420,16 @@ const FlxAnimationStep *FlxAnimTracker::FindAnimation(int64 hash) const
 }
 
 void FlxAnimTracker::Update(std::string_view encqueue) {
-	check(!encqueue.empty());
-	
+	// An empty encqueue represents a blank queue: one step with hash=0, empty body.
+	//
+	if (encqueue.empty()) {
+		if (AQ.Num() == 1 && AQ[0].Hash == 0) return;
+		Changed = true;
+		AQ.Empty();
+		AQ.Emplace(0, std::string_view());
+		return;
+	}
+
 	// If the first hash matches, we don't bother updating at all.
 	//
 	FlxAnimQueueDecoder decoder(encqueue);