Return value of DEV_RW not correctly checked in DOS1 mode

[S0urceror]

The following use-case:

• A 32Kb .COM file is loaded in MSX DOS 1.0
• Nextor on MSX1 without built-in DISKROM
• Start address in page 0 => 0x0100
• End address in page 2 => 0x8100

In DRV.MAC:

• Since the above file (partly) has to be loaded in page1 it uses: DIO_RD_LOOP
• After:

	ld	ix,DV_DSKIO##	;Or DEV_RW (they are at the same address)
	ex	af,af'
	ld	a,DV_BANK##
	call	CALBNK##
	jr	nc,DIO_RD_OK

• It checks for no-carry but the spec for DEV_RW only says to return an error-code in A
• It should be:

	ld	ix,DV_DSKIO##	;Or DEV_RW (they are at the same address)
	ex	af,af'
	ld	a,DV_BANK##
	call	CALBNK##
	and a
	jr	z,DIO_RD_OK

For now, I adapted my driver to set carry when A>0. And the problem is now solved.

A very special border-case I would call this.

I think DRV.MAC: DIO_RD_LOOP has to check the contents of A like CONV_ERR does for DIO_NOP1.

[S0urceror]

Created a PR.