Fixed crash on server stop.
Fixed crash on server stop.

The entity destructors called through chunkmap destructor and chunk destructor were accessing the world which was in an already invalid state (half-destroyed).
Fixed by destroying chunkmap explicitly and providing a nullptr check in the HasEntity() function.

ionux/MCServer,zackp30/cuberite,birkett/cuberite,johnsoch/cuberite,ionux/MCServer,SamOatesPlugins/cuberite,mc-server/MCServer,SamOatesPlugins/cuberite,Fighter19/cuberite,bendl/cuberite,Haxi52/cuberite,mjssw/cuberite,nevercast/cuberite,nichwall/cuberite,linnemannr/MCServer,kevinr/cuberite,Schwertspize/cuberite,nichwall/cuberite,zackp30/cuberite,thetaeo/cuberite,nichwall/cuberite,Howaner/MCServer,HelenaKitty/EbooMC,linnemannr/MCServer,bendl/cuberite,zackp30/cuberite,marvinkopf/cuberite,nounoursheureux/MCServer,birkett/cuberite,Schwertspize/cuberite,electromatter/cuberite,tonibm19/cuberite,Tri125/MCServer,Howaner/MCServer,birkett/MCServer,QUSpilPrgm/cuberite,Frownigami1/cuberite,kevinr/cuberite,birkett/MCServer,mmdk95/cuberite,nevercast/cuberite,mc-server/MCServer,HelenaKitty/EbooMC,nounoursheureux/MCServer,Fighter19/cuberite,Altenius/cuberite,mjssw/cuberite,jammet/MCServer,nichwall/cuberite,Frownigami1/cuberite,mjssw/cuberite,nounoursheureux/MCServer,thetaeo/cuberite,nicodinh/cuberite,birkett/cuberite,nicodinh/cuberite,tonibm19/cuberite,nevercast/cuberite,Altenius/cuberite,tonibm19/cuberite,Schwertspize/cuberite,guijun/MCServer,Tri125/MCServer,birkett/cuberite,marvinkopf/cuberite,linnemannr/MCServer,Schwertspize/cuberite,jammet/MCServer,HelenaKitty/EbooMC,electromatter/cuberite,ionux/MCServer,nevercast/cuberite,HelenaKitty/EbooMC,mc-server/MCServer,thetaeo/cuberite,linnemannr/MCServer,SamOatesPlugins/cuberite,kevinr/cuberite,nounoursheureux/MCServer,Howaner/MCServer,Howaner/MCServer,linnemannr/MCServer,birkett/MCServer,nicodinh/cuberite,mjssw/cuberite,tonibm19/cuberite,kevinr/cuberite,marvinkopf/cuberite,Tri125/MCServer,mmdk95/cuberite,Tri125/MCServer,SamOatesPlugins/cuberite,birkett/cuberite,birkett/MCServer,johnsoch/cuberite,linnemannr/MCServer,birkett/cuberite,tonibm19/cuberite,bendl/cuberite,Frownigami1/cuberite,guijun/MCServer,nevercast/cuberite,bendl/cuberite,Haxi52/cuberite,birkett/MCServer,thetaeo/cuberite,Haxi52/cuberite,mmdk95/cuberite,nicodinh/cuberite,mmdk95/cuberite,ionux/MCServer,ionux/MCServer,nounoursheureux/MCServer,nicodinh/cuberite,mc-server/MCServer,Tri125/MCServer,marvinkopf/cuberite,Frownigami1/cuberite,Howaner/MCServer,electromatter/cuberite,Fighter19/cuberite,birkett/MCServer,Haxi52/cuberite,kevinr/cuberite,Schwertspize/cuberite,Fighter19/cuberite,nounoursheureux/MCServer,Howaner/MCServer,Fighter19/cuberite,Fighter19/cuberite,QUSpilPrgm/cuberite,ionux/MCServer,QUSpilPrgm/cuberite,Altenius/cuberite,QUSpilPrgm/cuberite,mc-server/MCServer,mmdk95/cuberite,zackp30/cuberite,marvinkopf/cuberite,mmdk95/cuberite,Altenius/cuberite,thetaeo/cuberite,tonibm19/cuberite,jammet/MCServer,guijun/MCServer,guijun/MCServer,electromatter/cuberite,nichwall/cuberite,marvinkopf/cuberite,kevinr/cuberite,electromatter/cuberite,electromatter/cuberite,guijun/MCServer,Frownigami1/cuberite,johnsoch/cuberite,nicodinh/cuberite,mc-server/MCServer,guijun/MCServer,jammet/MCServer,QUSpilPrgm/cuberite,mjssw/cuberite,bendl/cuberite,jammet/MCServer,zackp30/cuberite,mjssw/cuberite,jammet/MCServer,Tri125/MCServer,johnsoch/cuberite,thetaeo/cuberite,HelenaKitty/EbooMC,SamOatesPlugins/cuberite,Haxi52/cuberite,zackp30/cuberite,Haxi52/cuberite,Altenius/cuberite,johnsoch/cuberite,nichwall/cuberite,nevercast/cuberite,QUSpilPrgm/cuberite