Using a path of "." with open_file_dialog on windows causes silent exit with return of None

[tbeckley]

Trying to use this library, I saw the "path" variable and assumed from the name it meant the path of the directory to open by default. I put in . to indicate the current working directory of the executable. This causes the dialog box to not even open and silently return None. IMHO this should be cleared up in one of three ways:

1. Rename the variable to "file_name" or something similar
2. Document the behaviour somewhere
3. Special case problem inputs and catch at the rust level