If we fail to open the settings file, display a message if it existed

[zadjii-msft]

A follow up from #1325.

In #1325's case, the file did exist, but we failed to open it. In this case, we should display some sort of error dialog to the user, instead of blowing away the user settings with the defaults.

[jj10133]

Hi Sir @zadjii-msft I would like to ask you there's a method ValidateProfilesExist() and ValidateDefaultProfileExists() which sets the default profile even if there's no profile. So I would like to ask you that do i make a separate method to show up the dialog or change this method.

[zadjii-msft]

If I were going to implement this, I'd honestly not touch either of those. CascadiaSettings::_ReadFile is the method that reads the settings file - I'd first figure out what HRESULT is thrown for a failure to read the file. Then, I'd modify App::_TryLoadSettings() to catch that exception, and check the HRESULT it catches. I believe right now, if it catches any HRESULT I think it assumes that's a JSON parse exception, but it won't always be. I'd add code to handle that exception specifically, and display a different message. You'd need to add another string to Resources.resw as well, so the message could be localized.