Fix crash resulting from bad month check in core_bind.cpp
Fix crash resulting from bad month check in core_bind.cpp

Also, make it clear that day is 0-based. This might cause very slight differcies in existing games.
Fixes #18221

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