Prevent crash on focus change when no valid next control has been found.
Prevent crash on focus change when no valid next control has been found.

Fixes the crash discussed in #6714.

firefly2442/godot,DmitriySalnikov/godot,morrow1nd/godot,ageazrael/godot,firefly2442/godot,RebelliousX/Go_Dot,Marqin/godot,DmitriySalnikov/godot,RandomShaper/godot,okamstudio/godot,tomreyn/godot,sanikoyes/godot,Valentactive/godot,akien-mga/godot,Max-Might/godot,DmitriySalnikov/godot,sanikoyes/godot,Faless/godot,groud/godot,godotengine/godot,ex/godot,groud/godot,godotengine/godot,honix/godot,josempans/godot,josempans/godot,vnen/godot,ex/godot,groud/godot,MarianoGnu/godot,tomreyn/godot,guilhermefelipecgs/godot,Zylann/godot,ZuBsPaCe/godot,josempans/godot,MarianoGnu/godot,Paulloz/godot,guilhermefelipecgs/godot,Marqin/godot,Valentactive/godot,Paulloz/godot,vkbsb/godot,RebelliousX/Go_Dot,morrow1nd/godot,MarianoGnu/godot,godotengine/godot,Shockblast/godot,josempans/godot,ageazrael/godot,ex/godot,Shockblast/godot,FateAce/godot,zicklag/godot,Zylann/godot,BastiaanOlij/godot,Paulloz/godot,zicklag/godot,josempans/godot,Zylann/godot,sanikoyes/godot,Max-Might/godot,groud/godot,okamstudio/godot,Valentactive/godot,Faless/godot,Valentactive/godot,RandomShaper/godot,ex/godot,vnen/godot,ZuBsPaCe/godot,vnen/godot,Paulloz/godot,BastiaanOlij/godot,NateWardawg/godot,jejung/godot,DmitriySalnikov/godot,MarianoGnu/godot,zicklag/godot,Brickcaster/godot,ficoos/godot,RebelliousX/Go_Dot,ageazrael/godot,tomreyn/godot,zicklag/godot,honix/godot,exabon/godot,Zylann/godot,Marqin/godot,vnen/godot,Paulloz/godot,zicklag/godot,RandomShaper/godot,RebelliousX/Go_Dot,Paulloz/godot,ageazrael/godot,akien-mga/godot,Brickcaster/godot,vkbsb/godot,sanikoyes/godot,ficoos/godot,Shockblast/godot,groud/godot,RebelliousX/Go_Dot,sanikoyes/godot,mcanders/godot,guilhermefelipecgs/godot,zicklag/godot,Faless/godot,NateWardawg/godot,Valentactive/godot,Shockblast/godot,Marqin/godot,mcanders/godot,mcanders/godot,RandomShaper/godot,josempans/godot,FateAce/godot,ZuBsPaCe/godot,Faless/godot,BastiaanOlij/godot,godotengine/godot,okamstudio/godot,n-pigeon/godot,jejung/godot,NateWardawg/godot,RandomShaper/godot,exabon/godot,guilhermefelipecgs/godot,mcanders/godot,n-pigeon/godot,Max-Might/godot,Marqin/godot,tomreyn/godot,MarianoGnu/godot,okamstudio/godot,n-pigeon/godot,jejung/godot,MrMaidx/godot,BastiaanOlij/godot,vnen/godot,Paulloz/godot,ZuBsPaCe/godot,Valentactive/godot,ZuBsPaCe/godot,ageazrael/godot,FateAce/godot,MrMaidx/godot,pkowal1982/godot,okamstudio/godot,morrow1nd/godot,Brickcaster/godot,jejung/godot,akien-mga/godot,honix/godot,Shockblast/godot,guilhermefelipecgs/godot,okamstudio/godot,akien-mga/godot,sanikoyes/godot,morrow1nd/godot,n-pigeon/godot,firefly2442/godot,Marqin/godot,FateAce/godot,firefly2442/godot,Faless/godot,honix/godot,mcanders/godot,MarianoGnu/godot,vkbsb/godot,exabon/godot,Shockblast/godot,NateWardawg/godot,okamstudio/godot,mcanders/godot,Zylann/godot,pkowal1982/godot,RebelliousX/Go_Dot,exabon/godot,firefly2442/godot,okamstudio/godot,ageazrael/godot,MarianoGnu/godot,ex/godot,vnen/godot,morrow1nd/godot,ZuBsPaCe/godot,ficoos/godot,okamstudio/godot,ageazrael/godot,akien-mga/godot,NateWardawg/godot,honix/godot,vkbsb/godot,n-pigeon/godot,godotengine/godot,vkbsb/godot,exabon/godot,NateWardawg/godot,MrMaidx/godot,firefly2442/godot,honix/godot,NateWardawg/godot,firefly2442/godot,Faless/godot,n-pigeon/godot,okamstudio/godot,RandomShaper/godot,Max-Might/godot,sanikoyes/godot,DmitriySalnikov/godot,guilhermefelipecgs/godot,ex/godot,Max-Might/godot,MarianoGnu/godot,vkbsb/godot,ex/godot,pkowal1982/godot,Shockblast/godot,BastiaanOlij/godot,pkowal1982/godot,vnen/godot,godotengine/godot,Zylann/godot,akien-mga/godot,Brickcaster/godot,jejung/godot,RandomShaper/godot,Brickcaster/godot,BastiaanOlij/godot,MrMaidx/godot,ficoos/godot,Valentactive/godot,ex/godot,FateAce/godot,guilhermefelipecgs/godot,godotengine/godot,josempans/godot,ZuBsPaCe/godot,exabon/godot,pkowal1982/godot,DmitriySalnikov/godot,ZuBsPaCe/godot,ficoos/godot,Zylann/godot,akien-mga/godot,akien-mga/godot,DmitriySalnikov/godot,morrow1nd/godot,godotengine/godot,pkowal1982/godot,vkbsb/godot,josempans/godot,BastiaanOlij/godot,pkowal1982/godot,Shockblast/godot,Zylann/godot,tomreyn/godot,firefly2442/godot,guilhermefelipecgs/godot,n-pigeon/godot,sanikoyes/godot,Brickcaster/godot,pkowal1982/godot,ficoos/godot,groud/godot,vkbsb/godot,MrMaidx/godot,Valentactive/godot,Max-Might/godot,Faless/godot,MrMaidx/godot,BastiaanOlij/godot,FateAce/godot,NateWardawg/godot,Brickcaster/godot,vnen/godot,NateWardawg/godot,jejung/godot,Faless/godot