nuget: bump UnicornEngine.Unicorn (#4459)

Bumps [UnicornEngine.Unicorn](https://github.com/unicorn-engine/unicorn) from 2.0.2-rc1-9c9356d to 2.0.2-rc1-a913199.
- [Release notes](https://github.com/unicorn-engine/unicorn/releases)
- [Changelog](https://github.com/unicorn-engine/unicorn/blob/master/ChangeLog)
- [Commits](https://github.com/unicorn-engine/unicorn/commits)

---
updated-dependencies:
- dependency-name: UnicornEngine.Unicorn
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Directory.Packages.props

@@ -49,7 +49,7 @@
     <PackageVersion Include="System.Management" Version="7.0.0" />
     <PackageVersion Include="System.Net.NameResolution" Version="4.3.0" />
     <PackageVersion Include="System.Threading.ThreadPool" Version="4.3.0" />
-    <PackageVersion Include="UnicornEngine.Unicorn" Version="2.0.2-rc1-9c9356d" />
+    <PackageVersion Include="UnicornEngine.Unicorn" Version="2.0.2-rc1-a913199" />
     <PackageVersion Include="XamlNameReferenceGenerator" Version="1.5.1" />
   </ItemGroup>
 </Project>

Ryujinx.Ava/Modules/Updater/Updater.cs

@@ -506,6 +506,11 @@ namespace Ryujinx.Modules
 
                             Dispatcher.UIThread.Post(() =>
                             {
+                                if (tarEntry is null)
+                                {
+                                    return;
+                                }
+
                                 taskDialog.SetProgressBarState(GetPercentage(tarEntry.Size, inStream.Length), TaskDialogProgressState.Normal);
                             });
                         }