PeekByte() on parts of the Apple II system bus results in crash (scrolling in the hex editor)

If you load up the Apple II core, open the hex editor, swap the domain to the System Bus, and try scrolling to the bottom, Bizhawk will crash with the following exception:

   at Jellyfish.Virtu.DiskIIDrive.get_IsWriteProtected()
   at Jellyfish.Virtu.DiskIIController.ReadIoRegionC0C0(Int32 address)
   at Jellyfish.Virtu.Memory.ReadIoRegionC0C0(Int32 address)
   at Jellyfish.Virtu.Memory.ReadIoRegionC0CF(Int32 address)
   at Jellyfish.Virtu.Memory.Peek(Int32 address)
   at BizHawk.Emulation.Cores.Computers.AppleII.AppleII.<SetupMemoryDomains>b__85_2(Int64 addr) in C:\Users\Daniel\Documents\BizHawk\BizHawk.Emulation.Cores\Computers\AppleII\AppleII.IMemoryDomains.cs:line 44
   at BizHawk.Client.EmuHawk.HexEditor.MakeValue(Int32 dataSize, Int64 address, Boolean& is_cheat) in C:\Users\Daniel\Documents\BizHawk\BizHawk.Client.EmuHawk\tools\HexEditor\HexEditor.cs:line 603
   at BizHawk.Client.EmuHawk.HexEditor.GenerateMemoryViewString(Boolean forWindow) in C:\Users\Daniel\Documents\BizHawk\BizHawk.Client.EmuHawk\tools\HexEditor\HexEditor.cs:line 539
   at BizHawk.Client.EmuHawk.HexEditor.UpdateValues() in C:\Users\Daniel\Documents\BizHawk\BizHawk.Client.EmuHawk\tools\HexEditor\HexEditor.cs:line 156
   at BizHawk.Client.EmuHawk.ToolManager.UpdateAfter() in C:\Users\Daniel\Documents\BizHawk\BizHawk.Client.EmuHawk\tools\ToolManager.cs:line 445
   at BizHawk.Client.EmuHawk.ToolManager.UpdateToolsAfter(Boolean fromLua) in C:\Users\Daniel\Documents\BizHawk\BizHawk.Client.EmuHawk\tools\ToolManager.cs:line 673
   at BizHawk.Client.EmuHawk.MainForm.StepRunLoop_Core(Boolean force) in C:\Users\Daniel\Documents\BizHawk\BizHawk.Client.EmuHawk\MainForm.cs:line 2988
   at BizHawk.Client.EmuHawk.MainForm.ProgramRunLoop() in C:\Users\Daniel\Documents\BizHawk\BizHawk.Client.EmuHawk\MainForm.cs:line 483
   at BizHawk.Client.EmuHawk.Program.SubMain(String[] args) in C:\Users\Daniel\Documents\BizHawk\BizHawk.Client.EmuHawk\Program.cs:line 227

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