Added asserts for proper game state.
Added asserts for proper game state.

This is to help hunt #889.

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