getSaveFileName doesn't check for existing file if extension isn't entered and the save type is selected to be 'Text Files' on Windows platform

The implementation doesn't follow the Windows platform default behavior if 'Save as type:' is selected to be 'Text Files (*.txt)'

standarddialogs can be used to reproduce this issue.

Follow these steps.
1) Using notepad or some other application create a file called test.txt
2) In the StandardDialogs example navigate to that directory and verify that you see the file test.txt.
3) In the Save as type: Select *.txt
4) Type "test" as the filename.
5) Click save.

Expected result:
A dialog should be shown to ask about if one wants to replace an existing file.

Actual result:
No warning about overwriting an existing file is shown.

Note that the output is indicating that the file test.txt at that path was selected.

Note: Using the non-native dialog the extension .txt is not added to the file which is also unexpected behavior.