Bounds check.
 [rsc] --rw-rw-r-- M 724822 rsc sys 21668 Dec 22 12:44 sys/src/cmd/aux/vga/vesa.c
	/n/sourcesdump/2005/1222/plan9/sys/src/cmd/aux/vga/vesa.c:226,232 - 
	/n/sourcesdump/2005/1223/plan9/sys/src/cmd/aux/vga/vesa.c:226,233
	  	if(p){
	  		for(ep=p+1024; (p[0]!=0xFF || p[1]!=0xFF) && p<ep; p+=2){
	  			vbeprintmodeinfo(vbe, WORD(p), "");
	- 			did[WORD(p)] = 1;
	+ 			if(WORD(p) < nelem(did))
	+ 				did[WORD(p)] = 1;
	  		}
	  	}
	  	for(i=0x100; i<0x1FF; i++)