Crash in diagnostics wizard

Hi all,

reporting this issue for: 1.5.11 (ubuntu 18.04 lts)

Steps to reproduce the crash:

Help->trouble shooter Click through wizard until you get to the point where you can enable debugging
click on enable debugging

-> output on the console:

Traceback:
File "/usr/share/system-config-printer/troubleshoot/__init__.py", line 316, in _collect_answer
    answer = question.collect_answer ()
File "/usr/share/system-config-printer/troubleshoot/ErrorLogCheckpoint.py", line 143, in collect_answer
    self.op.run ()
File "/usr/share/system-config-printer/timedops.py", line 212, in run
    return self.thread.collect_result ()
File "/usr/share/system-config-printer/timedops.py", line 165, in collect_result
    raise self.exception
File "/usr/share/system-config-printer/timedops.py", line 153, in run
    self.result = self.target (*self.args, **self.kwargs)
File "/usr/share/system-config-printer/authconn.py", line 232, in <lambda>
    return lambda *args, **kwds: self._authloop (fname, fn, *args, **kwds)
File "/usr/share/system-config-printer/authconn.py", line 250, in _authloop
    result = fn.__call__ (*args, **kwds)
File "/usr/share/system-config-printer/cupspk.py", line 422, in getFile
    *args, **kwds)
File "/usr/share/system-config-printer/cupspk.py", line 112, in _call_with_pk_and_fallback
    return fallback_function(*args, **kwds)
TypeError: argument 2 must be str, not _io.BufferedRandom
Traceback:
File "/usr/share/system-config-printer/troubleshoot/__init__.py", line 113, in quit
    self.questions[self.current_page].cancel_operation ()
File "/usr/share/system-config-printer/troubleshoot/PrintTestPage.py", line 343, in cancel_operation
    self.answers['_authenticated_connection'] = self.authconn
AttributeError: 'PrintTestPage' object has no attribute 'answers'
Fatal Python error: PyEval_RestoreThread: NULL tstate

Thread 0x00007f8eef7fe700 (most recent call first):
  File "/usr/share/system-config-printer/timedops.py", line 157 in run
  File "/usr/lib/python3.6/threading.py", line 964 in _bootstrap_inner
  File "/usr/lib/python3.6/threading.py", line 888 in _bootstrap

Current thread 0x00007f8eeffff700 (most recent call first):
  File "/usr/share/system-config-printer/authconn.py", line 250 in _authloop
  File "/usr/share/system-config-printer/authconn.py", line 232 in <lambda>
  File "/usr/share/system-config-printer/troubleshoot/PrintTestPage.py", line 172 in get_jobs
  File "/usr/share/system-config-printer/timedops.py", line 153 in run
  File "/usr/lib/python3.6/threading.py", line 916 in _bootstrap_inner
  File "/usr/lib/python3.6/threading.py", line 884 in _bootstrap

Thread 0x00007f8ee59f5700 (most recent call first):
  File "/usr/lib/python3.6/threading.py", line 295 in wait
  File "/usr/lib/python3.6/queue.py", line 164 in get
  File "/usr/share/system-config-printer/asyncipp.py", line 101 in run
  File "/usr/lib/python3.6/threading.py", line 916 in _bootstrap_inner
  File "/usr/lib/python3.6/threading.py", line 884 in _bootstrap

Thread 0x00007f8f163c5740 (most recent call first):
  File "/usr/share/system-config-printer/timedops.py", line 206 in run
  File "/usr/share/system-config-printer/troubleshoot/PrintTestPage.py", line 184 in display
  File "/usr/share/system-config-printer/troubleshoot/__init__.py", line 299 in _display
  File "/usr/share/system-config-printer/troubleshoot/__init__.py", line 226 in _on_back_clicked
  File "/usr/share/system-config-printer/system-config-printer.py", line 2238 in main
  File "/usr/share/system-config-printer/system-config-printer.py", line 2264 in <module>

Crash happened when pressing "back" in the wizard.

OpenPrinting / system-config-printer

Crash in diagnostics wizard #141