Fixed ItemList indexing bug while selecting items.
Fixed ItemList indexing bug while selecting items.

Also added functionality for unselecting items in itemlist while clicking in empty space.
Fixes #5772.

firefly2442/godot,FateAce/godot,gau-veldt/godot,okamstudio/godot,Faless/godot,sanikoyes/godot,Shockblast/godot,groud/godot,ageazrael/godot,sanikoyes/godot,honix/godot,okamstudio/godot,n-pigeon/godot,TheHX/godot,josempans/godot,Zylann/godot,vkbsb/godot,vnen/godot,firefly2442/godot,guilhermefelipecgs/godot,vkbsb/godot,Valentactive/godot,pkowal1982/godot,exabon/godot,MrMaidx/godot,firefly2442/godot,huziyizero/godot,exabon/godot,DmitriySalnikov/godot,akien-mga/godot,Max-Might/godot,godotengine/godot,honix/godot,vnen/godot,Shockblast/godot,Marqin/godot,zicklag/godot,Faless/godot,Brickcaster/godot,okamstudio/godot,TheHX/godot,Faless/godot,ex/godot,BastiaanOlij/godot,exabon/godot,Shockblast/godot,pkowal1982/godot,Zylann/godot,gau-veldt/godot,jejung/godot,NateWardawg/godot,morrow1nd/godot,RandomShaper/godot,RebelliousX/Go_Dot,MarianoGnu/godot,jejung/godot,okamstudio/godot,Zylann/godot,josempans/godot,Zylann/godot,ex/godot,Valentactive/godot,ageazrael/godot,vkbsb/godot,NateWardawg/godot,morrow1nd/godot,honix/godot,zicklag/godot,gau-veldt/godot,okamstudio/godot,sanikoyes/godot,okamstudio/godot,godotengine/godot,okamstudio/godot,RandomShaper/godot,ficoos/godot,godotengine/godot,BastiaanOlij/godot,MarianoGnu/godot,tomreyn/godot,josempans/godot,ficoos/godot,Max-Might/godot,firefly2442/godot,TheHX/godot,MrMaidx/godot,honix/godot,n-pigeon/godot,n-pigeon/godot,Shockblast/godot,morrow1nd/godot,ZuBsPaCe/godot,MrMaidx/godot,exabon/godot,DmitriySalnikov/godot,jejung/godot,TheHX/godot,Shockblast/godot,rollenrolm/godot,gau-veldt/godot,Paulloz/godot,huziyizero/godot,DmitriySalnikov/godot,Valentactive/godot,pkowal1982/godot,DmitriySalnikov/godot,gau-veldt/godot,firefly2442/godot,NateWardawg/godot,ageazrael/godot,NateWardawg/godot,BastiaanOlij/godot,ex/godot,zicklag/godot,RebelliousX/Go_Dot,NateWardawg/godot,sanikoyes/godot,n-pigeon/godot,Paulloz/godot,Marqin/godot,jejung/godot,pkowal1982/godot,groud/godot,akien-mga/godot,okamstudio/godot,ZuBsPaCe/godot,Marqin/godot,Brickcaster/godot,Paulloz/godot,pixelpicosean/my-godot-2.1,godotengine/godot,jejung/godot,sanikoyes/godot,sanikoyes/godot,rollenrolm/godot,ageazrael/godot,MarianoGnu/godot,firefly2442/godot,ficoos/godot,ex/godot,Faless/godot,ZuBsPaCe/godot,okamstudio/godot,tomreyn/godot,Zylann/godot,BastiaanOlij/godot,josempans/godot,guilhermefelipecgs/godot,Marqin/godot,ficoos/godot,ZuBsPaCe/godot,guilhermefelipecgs/godot,BastiaanOlij/godot,RandomShaper/godot,Brickcaster/godot,Paulloz/godot,RebelliousX/Go_Dot,pkowal1982/godot,Zylann/godot,Marqin/godot,honix/godot,vkbsb/godot,okamstudio/godot,DmitriySalnikov/godot,guilhermefelipecgs/godot,morrow1nd/godot,RandomShaper/godot,tomreyn/godot,ZuBsPaCe/godot,Paulloz/godot,MrMaidx/godot,RandomShaper/godot,Shockblast/godot,godotengine/godot,NateWardawg/godot,MrMaidx/godot,vnen/godot,pixelpicosean/my-godot-2.1,Brickcaster/godot,zicklag/godot,rollenrolm/godot,mcanders/godot,Valentactive/godot,vkbsb/godot,josempans/godot,groud/godot,MarianoGnu/godot,ZuBsPaCe/godot,Paulloz/godot,ageazrael/godot,ZuBsPaCe/godot,guilhermefelipecgs/godot,vkbsb/godot,ageazrael/godot,RebelliousX/Go_Dot,firefly2442/godot,sanikoyes/godot,RandomShaper/godot,Marqin/godot,mcanders/godot,RebelliousX/Go_Dot,guilhermefelipecgs/godot,morrow1nd/godot,Paulloz/godot,groud/godot,Max-Might/godot,Valentactive/godot,godotengine/godot,akien-mga/godot,vnen/godot,vnen/godot,pixelpicosean/my-godot-2.1,RandomShaper/godot,Valentactive/godot,NateWardawg/godot,zicklag/godot,groud/godot,mcanders/godot,rollenrolm/godot,DmitriySalnikov/godot,MarianoGnu/godot,Faless/godot,Shockblast/godot,ex/godot,zicklag/godot,jejung/godot,ageazrael/godot,MarianoGnu/godot,Brickcaster/godot,Max-Might/godot,vnen/godot,FateAce/godot,ficoos/godot,guilhermefelipecgs/godot,vnen/godot,sanikoyes/godot,Max-Might/godot,rollenrolm/godot,akien-mga/godot,Faless/godot,huziyizero/godot,Brickcaster/godot,FateAce/godot,akien-mga/godot,godotengine/godot,pixelpicosean/my-godot-2.1,TheHX/godot,vnen/godot,DmitriySalnikov/godot,godotengine/godot,NateWardawg/godot,mcanders/godot,akien-mga/godot,ZuBsPaCe/godot,morrow1nd/godot,ex/godot,honix/godot,josempans/godot,vkbsb/godot,firefly2442/godot,huziyizero/godot,exabon/godot,MarianoGnu/godot,ex/godot,NateWardawg/godot,Faless/godot,exabon/godot,FateAce/godot,akien-mga/godot,MrMaidx/godot,FateAce/godot,Brickcaster/godot,guilhermefelipecgs/godot,mcanders/godot,Valentactive/godot,groud/godot,josempans/godot,BastiaanOlij/godot,ex/godot,Shockblast/godot,Faless/godot,RebelliousX/Go_Dot,n-pigeon/godot,tomreyn/godot,Max-Might/godot,pkowal1982/godot,Zylann/godot,pixelpicosean/my-godot-2.1,FateAce/godot,BastiaanOlij/godot,Zylann/godot,pkowal1982/godot,vkbsb/godot,tomreyn/godot,pkowal1982/godot,mcanders/godot,josempans/godot,Valentactive/godot,akien-mga/godot,MarianoGnu/godot,huziyizero/godot,ficoos/godot,BastiaanOlij/godot,n-pigeon/godot,n-pigeon/godot