bytes vs string traceback after edit conflict

[RogerHaase]

Use 2 browsers, login with the first browser, do not login with the second browser.

Edit an item with 1st browser but do not save/ok the item. Wait for edit locking timeout. Edit and save same item with the 2nd browser. Return to first browser and click save/ok.

2019-08-01 12:45:12,108 INFO werkzeug:122 127.0.0.1 "POST /+modify/Home HTTP/1.1" 500 -
Traceback (most recent call last):
  File "c:\git37\moin-venv-python\lib\site-packages\flask\app.py", line 2463, in __call__
    return self.wsgi_app(environ, start_response)
  File "c:\git37\moin-venv-python\lib\site-packages\flask\app.py", line 2449, in wsgi_app
    response = self.handle_exception(e)
  File "c:\git37\moin-venv-python\lib\site-packages\flask\app.py", line 1866, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "c:\git37\moin-venv-python\lib\site-packages\flask\_compat.py", line 39, in reraise
    raise value
  File "c:\git37\moin-venv-python\lib\site-packages\flask\app.py", line 2446, in wsgi_app
    response = self.full_dispatch_request()
  File "c:\git37\moin-venv-python\lib\site-packages\flask\app.py", line 1951, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "c:\git37\moin-venv-python\lib\site-packages\flask\app.py", line 1820, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "c:\git37\moin-venv-python\lib\site-packages\flask\_compat.py", line 39, in reraise
    raise value
  File "c:\git37\moin-venv-python\lib\site-packages\flask\app.py", line 1949, in full_dispatch_request
    rv = self.dispatch_request()
  File "c:\git37\moin-venv-python\lib\site-packages\flask\app.py", line 1935, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "c:\git37\moin\src\moin\apps\frontend\views.py", line 722, in modify_item
    ret = item.do_modify()
  File "c:\git37\moin\src\moin\items\__init__.py", line 1133, in do_modify
    data3 = diff3.text_merge(original_text, saved_text, data)
  File "c:\git37\moin\src\moin\utils\diff3.py", line 18, in text_merge
    return ''.join(result)
TypeError: sequence item 1: expected str instance, bytes found