Early exit when outdated Windows detected

src/Ryujinx/Program.cs

@@ -47,6 +47,7 @@ namespace Ryujinx.Ava
             if (OperatingSystem.IsWindows() && !OperatingSystem.IsWindowsVersionAtLeast(10, 0, 19041))
             {
                 _ = MessageBoxA(nint.Zero, "You are running an outdated version of Windows.\n\nRyujinx supports Windows 10 version 20H1 and newer.\n", $"Ryujinx {Version}", MbIconwarning);
+                return 0;
             }
 
             PreviewerDetached = true;