ZPM3 Drive Map Fix

- Workaround to make ZPM3 consider all drives (A-P) valid so that subsequent drive ASSIGNments work properly.

Source/CBIOS/cbios.asm

@@ -1171,6 +1171,11 @@ DSK_GETINF:
 	RLCA			; ... TO USE AS OFFSET INTO DRVMAP
 	CALL	ADDHLA		; ADD OFFSET
 	LD	D,(HL)		; D := UNIT
+	
+	LD	A,D		; PUT UNIT IN ACCUM
+	INC	A		; $FF -> $00
+	JR	Z,DSK_GETINF1	; HANDLE UNASSIGNED DRIVE LETTER
+	
 	INC	HL		; BUMP TO SLICE
 	LD	E,(HL)		; E := SLICE
 	INC	HL		; POINT TO DPH LSB
@@ -1178,9 +1183,11 @@ DSK_GETINF:
 	INC	HL		; POINT TO DPH MSB
 	LD	H,(HL)		; H := DPH MSB
 	LD	L,A		; L := DPH LSB
-	LD	A,H		; TEST FOR INVALID DPH
-	OR	L		; ... BY CHECKING FOR ZERO VALUE
-	JR	Z,DSK_GETINF1	; HANDLE ZERO DPH, DRIVE IS INVALID
+
+	;LD	A,H		; TEST FOR INVALID DPH
+	;OR	L		; ... BY CHECKING FOR ZERO VALUE
+	;JR	Z,DSK_GETINF1	; HANDLE ZERO DPH, DRIVE IS INVALID
+
 	XOR	A		; SET SUCCESS
 	RET
 ;
@@ -1198,7 +1205,7 @@ DSK_GETINF1:	; ERROR RETURN
 DSK_SELECT:
 	LD	B,E		; SAVE E IN B FOR NOW
 	CALL	DSK_GETINF	; GET D=UNIT, E=SLICE, HL=DPH ADDRESS
-	CALL	NZ,PANIC	; *DEBUG*
+	;CALL	NZ,PANIC	; *DEBUG*
 	RET	NZ		; RETURN IF INVALID DRIVE (A=1, NZ SET, HL=0)
 	PUSH	BC		; WE NEED  B LATER, SAVE ON STACK
 ;