Add null checks and fix dispatcher invocation in Theme

Added early returns if Application.Current is null in RefreshFrameAsync and SetBlurForWindowAsync to prevent null reference exceptions. Updated dispatcher access checks and ensured the correct method is invoked asynchronously for each case, improving robustness and reliability.

Author: Jack251970

Flow.Launcher.Core/Resource/Theme.cs

@@ -644,7 +644,8 @@ private void SetResizeBoarderThickness(Thickness? effectMargin)
         /// </summary>
         public async Task RefreshFrameAsync()
         {
-            if (Application.Current?.Dispatcher.CheckAccess() != true)
+            if (Application.Current == null) return;
+            if (!Application.Current.Dispatcher.CheckAccess())
             {
                 await Application.Current?.Dispatcher.InvokeAsync(RefreshFrameAsync);
                 return;
@@ -676,9 +677,10 @@ public async Task RefreshFrameAsync()
         /// </summary>
         public async Task SetBlurForWindowAsync()
         {
-            if (Application.Current?.Dispatcher.CheckAccess() != true)
+            if (Application.Current == null) return;
+            if (!Application.Current.Dispatcher.CheckAccess())
             {
-                await Application.Current?.Dispatcher.InvokeAsync(RefreshFrameAsync);
+                await Application.Current?.Dispatcher.InvokeAsync(SetBlurForWindowAsync);
                 return;
             }