Fix SettingWindow's LeftTop Position when first launch

[onesounds]

What's The PR

• Fixed getting stuck in the upper left corner when opening the settings window after the first launch.
• If Setting Window Position is null, center the screen.

I think I made it this stupid for a reason, but I can't remember.
Needs to be reviewed to see if null is acceptable.

Test Case

When you open the settings window after the first launch with no settings, it is displayed in the center of the screen.

[VictoriousRaptor]

It's tricky to dealing with the window. Like if I close the settings window when it's minimized, the next time I open it, it stays minimized.

[VictoriousRaptor]

I think I made it this stupid for a reason, but I can't remember.

Maybe because #1368 (comment)

Don't have much time to check but why is it null on first launch?

[onesounds]

I think I made it this stupid for a reason, but I can't remember.

Maybe because #1368 (comment)

Don't have much time to check but why is it null on first launch?

(I didn't know too so I looked it up)
The settings window doesn't have a default value on initial launch, so it seems to have done so.

+) ?? That's some weird code. Why did I write that? (I tested it and it works)

[onesounds]

Fixed. (I think I wrote the code while drunk.)