Hang if mb-audit run with 80-col firmware enabled

[tomcw]

1.56 OK, but regression at 1.57 (and 1.58).
Same for: //e or Enhanced //e firmware.

Repro:

• s4=MB-C, s5=empty
  • or s4=empty, s5=MB-C
  • or s3=MB-C, s4+s5=empty
• Boot mb-audit
• F to drop to BASIC
• PR#3
• RUN and then select A
• it'll hang
  • or if running the VS debugger may assert in GetOpcodeCyclesForRead(), and (with s4=MB-C) in IORead(): PC=C404 and nAddr=C404

[tomcw]

s4=MB-C, s5=empty

g from debugger
PR#3, RUN, and select A

"Stop reason: PC reads from floating bus or I/O memory"
PC=$C307
LBR = $FDED

FDED: JMP ($0036) ; COUT, where (36)=$C307

Stack: 76 9A 02 2B [00] C2 C0
Return address: 9A77 - not within the MBA code space!
Return address: 2B03 - inside Print
(00 is from PHA)
Return address: 20C3 - inside Display

After RESET,
(36)=$FDF0
After PR#3
(36)=$C307