Changed API for checking titlebar customization availability

Author: d2dyno1

Diff for: SecureFolderFS.WinUI/Helpers/ThemeHelper.cs

@@ -58,7 +58,7 @@ public void UpdateTheme()
             {
                 case ApplicationTheme.Dark:
                 case ApplicationTheme.Light:
-                    if (_appWindow.TitleBar is not null)
+                    if (AppWindowTitleBar.IsCustomizationSupported())
                     {
                         _appWindow.TitleBar.ButtonHoverBackgroundColor = (Color)Application.Current.Resources["SystemBaseLowColor"];
                         _appWindow.TitleBar.ButtonForegroundColor = (Color)Application.Current.Resources["SystemBaseHighColor"];

Diff for: SecureFolderFS.WinUI/Windows/MainWindow.xaml.cs

@@ -42,7 +42,7 @@ private void EnsureEarlyWindow()
             // Set title
             AppWindow.Title = "SecureFolderFS";
 
-            if (AppWindow.TitleBar is not null)
+            if (AppWindowTitleBar.IsCustomizationSupported())
             {
                 // Extend title bar
                 AppWindow.TitleBar.ExtendsContentIntoTitleBar = true;