Don't use -1 as indicator in EntityTracker1_9#getVehicle

Author: FlorianMichael

common/src/main/java/com/viaversion/viarewind/protocol/v1_9to1_8/rewriter/EntityPacketRewriter1_9.java

@@ -324,11 +324,12 @@ public void register() {
 			public void register() {
 				handler(wrapper -> {
 					final EntityTracker1_9 tracker = wrapper.user().getEntityTracker(Protocol1_9To1_8.class);
-					final int vehicle = tracker.getVehicle(tracker.clientEntityId());
-					if (vehicle == -1) {
+					final Integer vehicle = tracker.getVehicle(tracker.clientEntityId());
+					if (vehicle == null) {
 						wrapper.cancel();
-					}
-					wrapper.write(Types.VAR_INT, vehicle);
+					} else {
+                        wrapper.write(Types.VAR_INT, vehicle);
+                    }
 				});
 				map(Types.DOUBLE, Protocol1_9To1_8.DOUBLE_TO_INT_TIMES_32); // X
 				map(Types.DOUBLE, Protocol1_9To1_8.DOUBLE_TO_INT_TIMES_32); // Y

common/src/main/java/com/viaversion/viarewind/protocol/v1_9to1_8/rewriter/PlayerPacketRewriter1_9.java

@@ -421,9 +421,9 @@ public void register() {
 			final float forward = wrapper.passthrough(Types.FLOAT);
 
 			final EntityTracker1_9 tracker = wrapper.user().getEntityTracker(Protocol1_9To1_8.class);
-			final int vehicle = tracker.getVehicle(tracker.clientEntityId());
+			final Integer vehicle = tracker.getVehicle(tracker.clientEntityId());
 
-			if (vehicle != -1 && tracker.entityType(vehicle) == EntityTypes1_9.EntityType.BOAT) {
+			if (vehicle != null && tracker.entityType(vehicle) == EntityTypes1_9.EntityType.BOAT) {
 				final PacketWrapper paddleBoat = PacketWrapper.create(ServerboundPackets1_9.PADDLE_BOAT, wrapper.user());
 				paddleBoat.write(Types.BOOLEAN, forward != 0.0f || sideways < 0.0f);
 				paddleBoat.write(Types.BOOLEAN, forward != 0.0f || sideways > 0.0f);

common/src/main/java/com/viaversion/viarewind/protocol/v1_9to1_8/storage/EntityTracker1_9.java

@@ -74,11 +74,11 @@ public boolean isInsideVehicle(final int id) {
 		return false;
 	}
 
-	public int getVehicle(final int passenger) {
+	public Integer getVehicle(final int passenger) {
 		for (Map.Entry<Integer, IntList> vehicle : vehicles.int2ObjectEntrySet()) {
 			if (vehicle.getValue().contains(passenger)) return vehicle.getKey();
 		}
-		return -1;
+		return null;
 	}
 
 	public Int2IntMap getStatus() {