visualize fails for certain UIImage pointers

[cbowns]

(Refs #205 and #177 )

Swift 4 code in Xcode 9.2 running on an iOS 10.3 device. I have a UIImage? I'm trying to visualize from the device, and it sometimes fails. (I don't know if it's related to the image optional or not: sometimes it works just fine!)

The error text is reliably the same:

(lldb) visualize image
error: error: Execution was interrupted, reason: breakpoint 1.1.
The process has been returned to the state before expression evaluation.
Traceback (most recent call last):
  File "/usr/local/opt/chisel/libexec/fblldb.py", line 83, in runCommand
    command.run(args, options)
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 178, in run
    _visualize(arguments[0])
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 150, in _visualize
    _showImage(target)
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 38, in _showImage
    imageBytesStartAddress = fb.evaluateExpression('(void *)[(id)' + imageDataAddress + ' bytes]')
TypeError: cannot concatenate 'str' and 'NoneType' objects

Even if I backtick it, or force-unwrap:

(lldb) visualize image
error: error: Execution was interrupted, reason: breakpoint 1.1.
The process has been returned to the state before expression evaluation.
Traceback (most recent call last):
  File "/usr/local/opt/chisel/libexec/fblldb.py", line 83, in runCommand
    command.run(args, options)
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 178, in run
    _visualize(arguments[0])
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 150, in _visualize
    _showImage(target)
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 38, in _showImage
    imageBytesStartAddress = fb.evaluateExpression('(void *)[(id)' + imageDataAddress + ' bytes]')
TypeError: cannot concatenate 'str' and 'NoneType' objects

(lldb) visualize image!
error: error: Execution was interrupted, reason: breakpoint 1.1.
The process has been returned to the state before expression evaluation.
Traceback (most recent call last):
  File "/usr/local/opt/chisel/libexec/fblldb.py", line 83, in runCommand
    command.run(args, options)
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 178, in run
    _visualize(arguments[0])
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 150, in _visualize
    _showImage(target)
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 38, in _showImage
    imageBytesStartAddress = fb.evaluateExpression('(void *)[(id)' + imageDataAddress + ' bytes]')
TypeError: cannot concatenate 'str' and 'NoneType' objects

(lldb) visualize `image`
error: error: Execution was interrupted, reason: breakpoint 1.1.
The process has been returned to the state before expression evaluation.
Traceback (most recent call last):
  File "/usr/local/opt/chisel/libexec/fblldb.py", line 83, in runCommand
    command.run(args, options)
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 178, in run
    _visualize(arguments[0])
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 150, in _visualize
    _showImage(target)
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 38, in _showImage
    imageBytesStartAddress = fb.evaluateExpression('(void *)[(id)' + imageDataAddress + ' bytes]')
TypeError: cannot concatenate 'str' and 'NoneType' objects

(lldb) visualize `image!`
error: error: Execution was interrupted, reason: breakpoint 1.1.
The process has been returned to the state before expression evaluation.
Traceback (most recent call last):
  File "/usr/local/opt/chisel/libexec/fblldb.py", line 83, in runCommand
    command.run(args, options)
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 178, in run
    _visualize(arguments[0])
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 150, in _visualize
    _showImage(target)
  File "/usr/local/Cellar/chisel/HEAD-2bc1bf6/libexec/commands/FBVisualizationCommands.py", line 38, in _showImage
    imageBytesStartAddress = fb.evaluateExpression('(void *)[(id)' + imageDataAddress + ' bytes]')
TypeError: cannot concatenate 'str' and 'NoneType' objects

[cbowns]

This is a dupe of #177