naive fix for #212408

[razielanarki]

A naive fix for #212408:

• added a simple this.isWindows check to line 835 of simpleFileDialog.ts
  (based on line 824 of the same file)

notes/toughts:

• the check is naive in it's current state:
  it assumes the this.isWindows also applies to the file service that provides the dirstat (i haven't had the time to investigate how the services instantiated by the dialog are related in code)
  this IMO may require more work either in simpleFileDialog (like trying to tocuh the destination in a Promise, and returning that) or the fileService (extra flags)
  → any comments, pointers, suggestions and help welcome! - this being my first PR to the codebase
• thus, the condition on line 845 may need to be split into 'read-only' and 'locked' checks
• also, the localization message with the key remoteFileDialog.validateReadonlyFolder should be renamed remoteFileDialog.validateLockedFolder for correctness, while possibly altering remoteFileDialog.validateReadonlyFolder or both to be more concise (if possible?)