Fix incorrect extension when filters is used

[shubham2892]

Running [dialog setAllowedFileTypes:file_types]; replaces the extension in nameFieldStringValue with first value in file_types variable however if [dialog setNameFieldStringValue:default_filename]; is run after setting the allowedFileTypes the extension initially passed with the default filename is retained. Explicitly setting setExtensionHidden makes sure that extension is shown everytime.
Screenshots to confirm that issue is fixed:

Code:

   const {dialog} = require('electron')
   dialog.showSaveDialog(mainWindow, {
     defaultPath:'/tmp/test.jpg',
     filters: [
       { name: 'Image', extensions: ['jpg', 'jpeg', 'png', 'gif'] }
     ]
   }, function(filename) {})

Result:

#9455

[shubham2892]

Not sure why this single test is failing on CI build, completely unrelated to changes I made. It's the same test that was failing in #9343 .

[shubham2892]

@kevinsawicki: Please have a look at your convenience. Thank you. 😄

[kevinsawicki]

Thanks for fixing this @shubham2892 👍