INT 62 u - FGDRIVER v4.02 - "FG_XVIEW" - CONVERT VIEWPORT COORDINATE
	AX = 00E3h
	BX = horizontal viewport coordinate
Return: AX = screen space X coordinate corresponding to supplied coordinate
Notes:	the FGDRIVER functions are rearranged with each major release, but
	  their parameters do not change (see #03474 at AX=0000h)
	if no viewport has been defined, the returned coordinate will be the
	  same as the viewport coordinate
SeeAlso: AX=00E2h,AX=00E6h