add ENTITY_NONE, ENTITY_AUTO reserved entity id & update player.set_entity(...)

src/objects/Player.hpp

@@ -54,7 +54,7 @@ class Player : public Serializable {
     bool infiniteItems = true;
     bool instantDestruction = true;
     bool loadingChunks = true;
-    entityid_t eid;
+    entityid_t eid = ENTITY_AUTO;
     entityid_t selectedEid = 0;
 
     glm::vec3 rotation {};