Fix hotbar slot changing when the player's hand is updated

The default value is 0.
-1 seems to leave the selected hotbar slot unchanged.

connector/src/main/java/org/geysermc/connector/entity/LivingEntity.java

@@ -83,6 +83,7 @@ public class LivingEntity extends Entity {
         MobEquipmentPacket mobEquipmentPacket = new MobEquipmentPacket();
         mobEquipmentPacket.setRuntimeEntityId(geyserId);
         mobEquipmentPacket.setItem(hand);
+        mobEquipmentPacket.setHotbarSlot(-1);
 
         session.getUpstream().sendPacket(armorEquipmentPacket);
         session.getUpstream().sendPacket(mobEquipmentPacket);