DesktopFileChooser does not release resouces used by fileDialog

[Anton-Samarskyi]

I tried to use DesktopFileChooser in my app and noticed that some thread is still present after application is closed. I figured out that it's due to missing dispose call on fileDialog in DesktopFileChooser.

The fix looks pretty simple (I checked it locally):
fileDialog.dispose();
But better to do that in finally block.

[Anton-Samarskyi]

Please take a look:
#10