[Settings] [Advanced Paste] Upgrade advanced paste settings safely to fix settings ui crash (#44862)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request
This pull request makes a minor fix in the `AdvancedPasteViewModel`
constructor to ensure the correct settings repository is used for null
checking. The change improves code correctness by verifying
`advancedPasteSettingsRepository` instead of the generic
`settingsRepository`.

- Fixed null check to use `advancedPasteSettingsRepository` instead of
`settingsRepository` in the `AdvancedPasteViewModel` constructor for
more accurate validation.
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## PR Checklist

- [x] Closes: #44835
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issues) -->
- [x] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [x] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
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- [ ] **Documentation updated:** If checked, please file a pull request
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and link it here: #xxx

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## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/settings-ui/Settings.UI/ViewModels/AdvancedPasteViewModel.cs

@@ -76,16 +76,24 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
 
             GeneralSettingsConfig = settingsRepository.SettingsConfig;
 
-            // To obtain the settings configurations of Fancy zones.
-            ArgumentNullException.ThrowIfNull(settingsRepository);
+            // To obtain the settings configurations of Advanced Paste.
+            ArgumentNullException.ThrowIfNull(advancedPasteSettingsRepository);
 
             _dispatcherQueue = DispatcherQueue.GetForCurrentThread();
 
             _settingsUtils = settingsUtils ?? throw new ArgumentNullException(nameof(settingsUtils));
 
-            ArgumentNullException.ThrowIfNull(advancedPasteSettingsRepository);
+            _advancedPasteSettings = advancedPasteSettingsRepository.SettingsConfig ?? throw new ArgumentException("SettingsConfig cannot be null", nameof(advancedPasteSettingsRepository));
 
-            _advancedPasteSettings = advancedPasteSettingsRepository.SettingsConfig;
+            if (_advancedPasteSettings.Properties is null)
+            {
+                throw new ArgumentException("AdvancedPasteSettings.Properties cannot be null", nameof(advancedPasteSettingsRepository));
+            }
+
+            // Ensure AdditionalActions and CustomActions are initialized to prevent null reference exceptions
+            // This handles legacy settings files that may be missing these properties
+            _advancedPasteSettings.Properties.AdditionalActions ??= new AdvancedPasteAdditionalActions();
+            _advancedPasteSettings.Properties.CustomActions ??= new AdvancedPasteCustomActions();
 
             AttachConfigurationHandlers();
 
@@ -93,7 +101,7 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
             SendConfigMSG = ipcMSGCallBackFunc;
 
             _additionalActions = _advancedPasteSettings.Properties.AdditionalActions;
-            _customActions = _advancedPasteSettings.Properties.CustomActions.Value;
+            _customActions = _advancedPasteSettings.Properties.CustomActions.Value ?? new ObservableCollection<AdvancedPasteCustomAction>();
 
             SetupSettingsFileWatcher();
 
@@ -469,7 +477,13 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
 
         public PasteAIConfiguration PasteAIConfiguration
         {
-            get => _advancedPasteSettings.Properties.PasteAIConfiguration;
+            get
+            {
+                // Ensure PasteAIConfiguration is never null for XAML binding
+                _advancedPasteSettings.Properties.PasteAIConfiguration ??= new PasteAIConfiguration();
+                return _advancedPasteSettings.Properties.PasteAIConfiguration;
+            }
+
             set
             {
                 if (!ReferenceEquals(value, _advancedPasteSettings.Properties.PasteAIConfiguration))