Description of problem:

  When attempting to save a session with the keyboard
shortcut Control-s, bpython will crash.


Version-Release number of selected component (if applicable):

  0.3.0-3.fc29.noarch


How reproducible:

  Always.


Steps to Reproduce:

1. From bash, run 'bpython3'
2. Press Control-S
3. Type 'print("hello")'
3. Enter 'hi' as the output file name.
4. Press enter.
5. See the traceback.
6. Run 'cat hi' and observe that the saved file is empty.


Actual results:

Traceback (most recent call last):
  File "/usr/bin/bpython3", line 11, in <module>
    load_entry_point('bpython==0.17.1', 'console_scripts', 'bpython')()
  File "/usr/lib/python3.7/site-packages/bpython/curtsies.py", line 191, in main
    exit_value = repl.mainloop(True, paste)
  File "/usr/lib/python3.7/site-packages/bpython/curtsies.py", line 123, in mainloop
    self.process_event_and_paint(e)
  File "/usr/lib/python3.7/site-packages/bpython/curtsies.py", line 90, in process_event_and_paint
    self.process_event(e)
  File "/usr/lib/python3.7/site-packages/bpython/curtsiesfrontend/repl.py", line 603, in process_event
    return self.process_key_event(e)
  File "/usr/lib/python3.7/site-packages/bpython/curtsiesfrontend/repl.py", line 679, in process_key_event
    return self.status_bar.process_event(e)
  File "/usr/lib/python3.7/site-packages/bpython/curtsiesfrontend/interaction.py", line 99, in process_event
    self.request_context.switch(line)
  File "/usr/lib/python3.7/site-packages/bpython/repl.py", line 845, in write2file
    f.write(stdout_text)


Expected results: 

  A non-empty file named hi should be created in the current directory with
the contents of the repl session, and you should then return to the bpython 
prompt.


Additional info:

  The variable stdout_text is not defined.