fix crash after click on MeshInstance with no owner
fix crash after click on MeshInstance with no owner

Due to how spatial selection works, after clicking on
MeshInstance that had no owner editor was crashing.

Paulloz/godot,vnen/godot,ageazrael/godot,ex/godot,RandomShaper/godot,sanikoyes/godot,akien-mga/godot,guilhermefelipecgs/godot,groud/godot,DmitriySalnikov/godot,okamstudio/godot,MarianoGnu/godot,akien-mga/godot,ex/godot,Shockblast/godot,Faless/godot,josempans/godot,n-pigeon/godot,vnen/godot,okamstudio/godot,MarianoGnu/godot,jejung/godot,Zylann/godot,honix/godot,godotengine/godot,MarianoGnu/godot,MarianoGnu/godot,NateWardawg/godot,zicklag/godot,Zylann/godot,mcanders/godot,josempans/godot,Paulloz/godot,NateWardawg/godot,Valentactive/godot,n-pigeon/godot,ex/godot,BastiaanOlij/godot,groud/godot,groud/godot,Faless/godot,RandomShaper/godot,godotengine/godot,BastiaanOlij/godot,BastiaanOlij/godot,guilhermefelipecgs/godot,zicklag/godot,NateWardawg/godot,pkowal1982/godot,RandomShaper/godot,guilhermefelipecgs/godot,n-pigeon/godot,groud/godot,ZuBsPaCe/godot,mcanders/godot,okamstudio/godot,zicklag/godot,FateAce/godot,Brickcaster/godot,Faless/godot,Zylann/godot,godotengine/godot,firefly2442/godot,MarianoGnu/godot,Paulloz/godot,ZuBsPaCe/godot,Shockblast/godot,okamstudio/godot,Faless/godot,josempans/godot,guilhermefelipecgs/godot,Shockblast/godot,vkbsb/godot,Brickcaster/godot,n-pigeon/godot,vkbsb/godot,BastiaanOlij/godot,okamstudio/godot,ZuBsPaCe/godot,BastiaanOlij/godot,vkbsb/godot,ZuBsPaCe/godot,Paulloz/godot,groud/godot,DmitriySalnikov/godot,guilhermefelipecgs/godot,ZuBsPaCe/godot,FateAce/godot,godotengine/godot,vnen/godot,jejung/godot,FateAce/godot,sanikoyes/godot,Brickcaster/godot,pkowal1982/godot,honix/godot,ZuBsPaCe/godot,okamstudio/godot,MarianoGnu/godot,mcanders/godot,RandomShaper/godot,josempans/godot,sanikoyes/godot,Brickcaster/godot,akien-mga/godot,honix/godot,jejung/godot,FateAce/godot,ex/godot,MarianoGnu/godot,DmitriySalnikov/godot,ZuBsPaCe/godot,Brickcaster/godot,sanikoyes/godot,sanikoyes/godot,firefly2442/godot,FateAce/godot,akien-mga/godot,firefly2442/godot,vkbsb/godot,josempans/godot,ageazrael/godot,vnen/godot,n-pigeon/godot,ex/godot,ageazrael/godot,sanikoyes/godot,akien-mga/godot,vnen/godot,vnen/godot,Paulloz/godot,guilhermefelipecgs/godot,pkowal1982/godot,firefly2442/godot,Shockblast/godot,honix/godot,BastiaanOlij/godot,Zylann/godot,mcanders/godot,okamstudio/godot,Valentactive/godot,okamstudio/godot,honix/godot,jejung/godot,Faless/godot,Zylann/godot,vkbsb/godot,godotengine/godot,ZuBsPaCe/godot,vnen/godot,godotengine/godot,pkowal1982/godot,DmitriySalnikov/godot,zicklag/godot,Valentactive/godot,Shockblast/godot,DmitriySalnikov/godot,Brickcaster/godot,ageazrael/godot,pkowal1982/godot,groud/godot,Valentactive/godot,mcanders/godot,Shockblast/godot,firefly2442/godot,firefly2442/godot,godotengine/godot,jejung/godot,DmitriySalnikov/godot,mcanders/godot,pkowal1982/godot,vkbsb/godot,vnen/godot,n-pigeon/godot,DmitriySalnikov/godot,Valentactive/godot,okamstudio/godot,firefly2442/godot,zicklag/godot,ageazrael/godot,godotengine/godot,BastiaanOlij/godot,MarianoGnu/godot,BastiaanOlij/godot,Shockblast/godot,sanikoyes/godot,josempans/godot,Shockblast/godot,NateWardawg/godot,honix/godot,RandomShaper/godot,Paulloz/godot,guilhermefelipecgs/godot,Valentactive/godot,Faless/godot,Brickcaster/godot,sanikoyes/godot,NateWardawg/godot,ex/godot,NateWardawg/godot,NateWardawg/godot,RandomShaper/godot,NateWardawg/godot,ageazrael/godot,Zylann/godot,firefly2442/godot,ageazrael/godot,guilhermefelipecgs/godot,Valentactive/godot,akien-mga/godot,Faless/godot,Valentactive/godot,okamstudio/godot,NateWardawg/godot,pkowal1982/godot,jejung/godot,ex/godot,RandomShaper/godot,Zylann/godot,FateAce/godot,akien-mga/godot,ex/godot,Faless/godot,n-pigeon/godot,josempans/godot,pkowal1982/godot,vkbsb/godot,zicklag/godot,Paulloz/godot,josempans/godot,akien-mga/godot,Zylann/godot,vkbsb/godot