Appveyor tests fails with timeout testing category_graph.py after file path validation done for T346417
**Current behaviour:**
The command line ``pwb category_graph -simulate`` produces the following input request
`Files exist for . Overwrite? ([y]es, [N]o):`
Note: `args` and `rest` are
`Namespace(to='', style='', depth=2, downsize=4) ['-simulate']`
Btw `pwb category_graph -simulate -to` fails with
```
Traceback (most recent call last):
File "D:\pwb\GIT\core\pwb.py", line 40, in <module>
sys.exit(main())
^^^^^^
File "D:\pwb\GIT\core\pwb.py", line 36, in main
runpy.run_path(str(path), run_name='__main__')
File "<frozen runpy>", line 291, in run_path
File "<frozen runpy>", line 98, in _run_module_code
File "<frozen runpy>", line 88, in _run_code
File "D:\pwb\GIT\core\pywikibot\scripts\wrapper.py", line 520, in <module>
main()
File "D:\pwb\GIT\core\pywikibot\scripts\wrapper.py", line 504, in main
if not execute():
^^^^^^^^^
File "D:\pwb\GIT\core\pywikibot\scripts\wrapper.py", line 491, in execute
run_python_file(filename, script_args, module)
File "D:\pwb\GIT\core\pywikibot\scripts\wrapper.py", line 147, in run_python_file
exec(compile(source, filename, 'exec', dont_inherit=True),
File "D:\pwb\GIT\core\scripts\category_graph.py", line 215, in <module>
if glob.glob(file_path + '.*'):
~~~~~~~~~~^~~~~~
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'
CRITICAL: Exiting due to uncaught exception TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'
```
**What should happen instead?**
Discard the input request for missing `from` option which is required (isn't it?)