Refactor code to make it easier to do 'nopredict' inside of any function without having a dependency on world model.

luprex/cpp/core/luasnap.cpp

@@ -85,7 +85,8 @@ void LuaSnap::deserialize(StreamBuffer *sb) {
     void *ud = sb->lua_reader_ud(len);
 
     // Call eris with the permanents table and passing the snapshot as a lua_Reader.
-    lua_getfield(state_, LUA_REGISTRYINDEX, "unpersist");
+    lua_pushstring(state_, "unpersist");
+    lua_rawget(state_, LUA_REGISTRYINDEX);
     eris_undump(state_, sb->lua_reader, ud);
     assert(lua_gettop(state_) == 2);