Don't modify DB while using `_embed`
Don't modify DB while using `_embed`

- We skip embedding nonexistent collections to avoid auto-creating them by lowdb
- We clone the object to avoid auto-saving embedded collection
androidgilbert/json-server,JulienBrks/json-server,whamsicore/json-server,rongself/json-server,anuragg1988/FakeAPI,songyaos/json-server,yangchenghu/json-server,claimsmall/json-server,no2key/json-server,codesdk/json-server,androidgilbert/json-server,legovaer/json-server,syzer/json-server,watermeion/json-server,liyocee/json-server,zhengcongzhen/json-server,zyggit/json-server,whamsicore/json-server,zhouwude/json-server,Leviathan777/json-server,watermeion/json-server,yihaojf/json-server,jkhaled/json-server,zhouwude/json-server,jjz/json-server,codesdk/json-server,Ribeiro/json-server,bhagatali/json-server,cycDroid/json-server,lancetw/json-server,tfrth/json-server,ZhouHengYi/json-server,xfstudio/json-server,jjz/json-server,anuragg1988/FakeAPI,syzer/json-server,lioonline/json-server,legovaer/json-server,jshiying/json-server,tfrth/json-server,kskgy/json-server,codevlabs/json-server,rongself/json-server,liveNo/json-server,petcai/json-server,lstNull/json-server,Volcanoscar/json-server,shawn-dsz/json-server,moneta-project/json-server,kskgy/json-server,ds0nt/json-server,codevlabs/json-server,Ribeiro/json-server,henser123/json-server,zhoule/json-server,JBusch/json-server,crazypoo/json-server,yangchenghu/json-server,dfsq/json-server,lstNull/json-server,moneta-project/json-server,sandyway/json-server,claimsmall/json-server,JulienBrks/json-server,songyaos/json-server,xfstudio/json-server,shawn-dsz/json-server,liveNo/json-server,lioonline/json-server,2947721120/json-server,Volcanoscar/json-server,lishengzxc/json-server,zhengcongzhen/json-server,JBusch/json-server,winston-misfit/json-server,dfsq/json-server,winston-misfit/json-server,lishengzxc/json-server,cycDroid/json-server,typicode/json-server,Leviathan777/json-server,sandyway/json-server,yihaojf/json-server,no2key/json-server,ds0nt/json-server,2947721120/json-server,crazypoo/json-server,henser123/json-server,typicode/json-server,jkhaled/json-server,ZhouHengYi/json-server,petcai/json-server,typicode/json-server,lancetw/json-server,jshiying/json-server,zhoule/json-server,bhagatali/json-server,zyggit/json-server,liyocee/json-server