INT 6F - HP Vectra EX-BIOS - "F_STR_GET_FREE_INDEX" - FIND FREE STRING INDEX
	AH = 40h
	BP = 0012h (driver ID of V_SYSTEM)
Return: AH = status (see #03744)
	BX = next free string index
	BP,DS destroyed
Desc:	get the next string index available to user programs
SeeAlso: AH=00h"HP Vectra",AH=42h/BP=0012h,AH=44h/BP=0012h,AH=46h/BP=0012h