fixes in case FindROOT does not find ROOT.
fixes in case FindROOT does not find ROOT.

This can happen when FindROOT.cmake is copied into a third party project
and cmake is run on a machine where ROOT is not installed.

georgtroska/root,zzxuanyuan/root-compressor-dummy,CristinaCristescu/root,karies/root,satyarth934/root,karies/root,satyarth934/root,satyarth934/root,gganis/root,abhinavmoudgil95/root,davidlt/root,veprbl/root,BerserkerTroll/root,mhuwiler/rootauto,karies/root,beniz/root,Y--/root,mhuwiler/rootauto,pspe/root,buuck/root,buuck/root,pspe/root,pspe/root,agarciamontoro/root,BerserkerTroll/root,beniz/root,davidlt/root,zzxuanyuan/root,olifre/root,beniz/root,root-mirror/root,karies/root,satyarth934/root,sawenzel/root,simonpf/root,zzxuanyuan/root,root-mirror/root,Y--/root,zzxuanyuan/root-compressor-dummy,simonpf/root,root-mirror/root,davidlt/root,zzxuanyuan/root-compressor-dummy,mhuwiler/rootauto,agarciamontoro/root,veprbl/root,sawenzel/root,buuck/root,BerserkerTroll/root,bbockelm/root,BerserkerTroll/root,satyarth934/root,satyarth934/root,georgtroska/root,gganis/root,beniz/root,abhinavmoudgil95/root,thomaskeck/root,root-mirror/root,gbitzes/root,gganis/root,georgtroska/root,bbockelm/root,satyarth934/root,abhinavmoudgil95/root,olifre/root,CristinaCristescu/root,thomaskeck/root,sawenzel/root,buuck/root,bbockelm/root,Y--/root,bbockelm/root,CristinaCristescu/root,davidlt/root,root-mirror/root,Y--/root,zzxuanyuan/root-compressor-dummy,veprbl/root,agarciamontoro/root,Y--/root,mhuwiler/rootauto,CristinaCristescu/root,abhinavmoudgil95/root,BerserkerTroll/root,root-mirror/root,buuck/root,zzxuanyuan/root,CristinaCristescu/root,BerserkerTroll/root,Y--/root,sawenzel/root,veprbl/root,davidlt/root,buuck/root,mhuwiler/rootauto,agarciamontoro/root,simonpf/root,thomaskeck/root,davidlt/root,georgtroska/root,gganis/root,root-mirror/root,gbitzes/root,davidlt/root,sawenzel/root,davidlt/root,agarciamontoro/root,simonpf/root,zzxuanyuan/root-compressor-dummy,pspe/root,gbitzes/root,bbockelm/root,bbockelm/root,thomaskeck/root,buuck/root,simonpf/root,karies/root,gbitzes/root,bbockelm/root,sawenzel/root,buuck/root,sawenzel/root,beniz/root,davidlt/root,lgiommi/root,Y--/root,CristinaCristescu/root,thomaskeck/root,olifre/root,simonpf/root,gganis/root,thomaskeck/root,veprbl/root,mhuwiler/rootauto,Y--/root,lgiommi/root,beniz/root,abhinavmoudgil95/root,satyarth934/root,georgtroska/root,zzxuanyuan/root,olifre/root,karies/root,buuck/root,satyarth934/root,lgiommi/root,root-mirror/root,zzxuanyuan/root,Y--/root,zzxuanyuan/root,zzxuanyuan/root,gbitzes/root,CristinaCristescu/root,mhuwiler/rootauto,root-mirror/root,bbockelm/root,beniz/root,agarciamontoro/root,veprbl/root,zzxuanyuan/root,zzxuanyuan/root,georgtroska/root,BerserkerTroll/root,abhinavmoudgil95/root,gbitzes/root,mhuwiler/rootauto,gganis/root,gbitzes/root,pspe/root,beniz/root,olifre/root,BerserkerTroll/root,sawenzel/root,olifre/root,zzxuanyuan/root-compressor-dummy,bbockelm/root,pspe/root,gbitzes/root,beniz/root,agarciamontoro/root,veprbl/root,veprbl/root,lgiommi/root,CristinaCristescu/root,pspe/root,root-mirror/root,lgiommi/root,beniz/root,olifre/root,lgiommi/root,buuck/root,bbockelm/root,lgiommi/root,veprbl/root,zzxuanyuan/root-compressor-dummy,CristinaCristescu/root,zzxuanyuan/root-compressor-dummy,georgtroska/root,olifre/root,abhinavmoudgil95/root,olifre/root,gganis/root,georgtroska/root,BerserkerTroll/root,simonpf/root,abhinavmoudgil95/root,karies/root,thomaskeck/root,Y--/root,root-mirror/root,simonpf/root,abhinavmoudgil95/root,abhinavmoudgil95/root,veprbl/root,zzxuanyuan/root,mhuwiler/rootauto,georgtroska/root,simonpf/root,sawenzel/root,mhuwiler/rootauto,satyarth934/root,agarciamontoro/root,zzxuanyuan/root,zzxuanyuan/root,CristinaCristescu/root,karies/root,karies/root,zzxuanyuan/root-compressor-dummy,BerserkerTroll/root,zzxuanyuan/root-compressor-dummy,zzxuanyuan/root-compressor-dummy,BerserkerTroll/root,satyarth934/root,gbitzes/root,gbitzes/root,karies/root,gganis/root,davidlt/root,pspe/root,Y--/root,olifre/root,veprbl/root,thomaskeck/root,georgtroska/root,simonpf/root,pspe/root,CristinaCristescu/root,gganis/root,sawenzel/root,sawenzel/root,karies/root,simonpf/root,gganis/root,thomaskeck/root,gbitzes/root,gganis/root,lgiommi/root,lgiommi/root,mhuwiler/rootauto,agarciamontoro/root,davidlt/root,georgtroska/root,pspe/root,agarciamontoro/root,lgiommi/root,olifre/root,thomaskeck/root,abhinavmoudgil95/root,bbockelm/root,lgiommi/root,beniz/root,pspe/root,buuck/root,agarciamontoro/root