Also return empty space on E80x.

I found a test program that cares about this:
8032.mem.prg from https://www.zimmers.net/anonftp/pub/cbm/pet/utilities/
It tests the 64K memory expansion and wants to see empty space at E800 if the
"I/O peek through" is enabled:

.C:096d  A9 CC       LDA #$CC	; enabled; i/o peek though; bank 3 and 1; no w/p
.C:096f  8D F0 FF    STA $FFF0
.C:0972  85 00       STA $00
.C:0974  AD 00 E8    LDA $E800	; I/O area but no chip selected
.C:0977  C9 E8       CMP #$E8
.C:0979  F0 07       BEQ $0982



git-svn-id: https://svn.code.sf.net/p/vice-emu/code/trunk@45467 379a1393-f5fb-40a0-bcee-ef074d9b53f7

vice/src/pet/petmem.c

@@ -901,7 +901,7 @@ static uint8_t read_io_e8(uint16_t addr)
                 last_access = crtc_read(addr);
             } /* fall through */
         case 0x00:
-            return last_access;
+            return addr >> 8;   /* empty space */
         default:                /* 0x30, 0x50, 0x60, 0x70, 0x90-0xf0 */
             if (addr & 0x10) {
                 v1 = pia1_read(addr);