INT 50 - Vanderaart TEXT WINDOWS, PC Thuis Shell - OPEN TEXT WINDOW

	AX = 0000h
	ES:BX -> name string or ES:0000h if none
	CH,CL = row,column of upper left corner
	DH,DL = row,column of lower right corner
Return: AX = window handle or
	    0000h if not installed
	    FFFFh on error
SeeAlso: AX=0001h,AX=0002h"TEXT WINDOWS"