Cancelling from the "load corpus" file chooser throws FileNotFoundError

[kvesik]

To reproduce:

1. Select "Load corpus" (either from the initialization window, or from within SLPAA if it is already open).
2. Click "cancel" on the file chooser dialog.
3. *** The GUI looks fine (just returns to the state it was in before you clicked "load corpus"), but terminal output shows a FileNotFoundError. Screen dump below.

Traceback (most recent call last):
  File "C:\Users\kvesik\Documents\School\RA-KCH\GitHub\SLPAA\src\main\python\main.py", line 8, in <module>
    exit_code = appctxt.run()
                ^^^^^^^^^^^^^
  File "C:\Users\kvesik\Documents\School\RA-KCH\GitHub\SLPAA\src\main\python\gui\app.py", line 15, in run
    return self.app.exec_()
           ^^^^^^^^^^^^^^^^
  File "C:\Users\kvesik\Documents\School\RA-KCH\GitHub\SLPAA\src\main\python\gui\decorator.py", line 41, in wrapper_check_unsaved_change
    func(self, event, *args, **kwargs)
  File "C:\Users\kvesik\Documents\School\RA-KCH\GitHub\SLPAA\src\main\python\gui\main_window.py", line 887, in on_action_load_corpus
    self.corpus = self.load_corpus_binary(file_name)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\kvesik\Documents\School\RA-KCH\GitHub\SLPAA\src\main\python\gui\main_window.py", line 850, in load_corpus_binary
    with open(path, 'rb') as f:
         ^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: ''