Fix failing test: Invalid background images not purged by validate
Fixes#6310: Background images only delete when using "Replace existing images" when new image(s) is found to replace them
when `ProviderManager.SaveMetadata` gets called before
`ProviderManager.AddParts`
```
Error Message:
System.ArgumentNullException : Value cannot be null. (Parameter 'source')
Stack Trace:
at System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
at System.Linq.Enumerable.Where[TSource](IEnumerable`1 source, Func`2 predicate)
at MediaBrowser.Providers.Manager.ProviderManager.SaveMetadata(BaseItem item, ItemUpdateType updateType, IEnumerable`1 savers) in D:\a\1\s\MediaBrowser.Providers\Manager\ProviderManager.cs:line 674
at MediaBrowser.Providers.Manager.ProviderManager.SaveMetadata(BaseItem item, ItemUpdateType updateType) in D:\a\1\s\MediaBrowser.Providers\Manager\ProviderManager.cs:line 655
at Emby.Server.Implementations.Library.LibraryManager.RunMetadataSavers(BaseItem item, ItemUpdateType updateReason) in D:\a\1\s\Emby.Server.Implementations\Library\LibraryManager.cs:line 2012
at Emby.Server.Implementations.Library.LibraryManager.UpdateItemsAsync(IReadOnlyList`1 items, BaseItem parent, ItemUpdateType updateReason, CancellationToken cancellationToken) in D:\a\1\s\Emby.Server.Implementations\Library\LibraryManager.cs:line 1970
at Emby.Server.Implementations.Library.LibraryManager.CreateRootFolder() in D:\a\1\s\Emby.Server.Implementations\Library\LibraryManager.cs:line 775
at Emby.Server.Implementations.Library.LibraryManager.get_RootFolder() in D:\a\1\s\Emby.Server.Implementations\Library\LibraryManager.cs:line 180
at Emby.Server.Implementations.IO.LibraryMonitor.Start() in D:\a\1\s\Emby.Server.Implementations\IO\LibraryMonitor.cs:line 135
at Emby.Server.Implementations.IO.LibraryMonitorStartup.RunAsync() in D:\a\1\s\Emby.Server.Implementations\IO\LibraryMonitorStartup.cs:line 26
at Emby.Server.Implementations.ApplicationHost.StartEntryPoints(IEnumerable`1 entryPoints, Boolean isBeforeStartup)+MoveNext() in D:\a\1\s\Emby.Server.Implementations\ApplicationHost.cs:line 541
at System.Threading.Tasks.Task.WhenAll(IEnumerable`1 tasks)
at Emby.Server.Implementations.ApplicationHost.RunStartupTasksAsync(CancellationToken cancellationToken) in D:\a\1\s\Emby.Server.Implementations\ApplicationHost.cs:line 525
at Jellyfin.Server.Integration.Tests.JellyfinApplicationFactory.CreateServer(IWebHostBuilder builder) in D:\a\1\s\tests\Jellyfin.Server.Integration.Tests\JellyfinApplicationFactory.cs:line 101
at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.EnsureServer()
at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateDefaultClient(DelegatingHandler[] handlers)
at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateDefaultClient(Uri baseAddress, DelegatingHandler[] handlers)
at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateClient(WebApplicationFactoryClientOptions options)
at Microsoft.AspNetCore.Mvc.Testing.WebApplicationFactory`1.CreateClient()
at Jellyfin.Server.Integration.Tests.OpenApiSpecTests.GetSpec_ReturnsCorrectResponse() in D:\a\1\s\tests\Jellyfin.Server.Integration.Tests\OpenApiSpecTests.cs:line 26
--- End of stack trace from previous location ---
```
If the lookup fails (due to a bad id in an nfo file for example), then
we had no indication of which directory failed, so the user can not
fix the problem.
Now we include the path in the error message such as:
MediaBrowser.Providers.TV.SeriesMetadataService: Error in
DummySeasonProvider for /media/x/y/z
and
MediaBrowser.Providers.Manager.ProviderManager:
TvdbSeriesImageProvider failed in GetImageInfos for type Series at
/media/x/y/z
Joe Rogers
Bond_009
Cody Robibero
Chris Tam
Fernando Fernández
Claus Vium
Rich Lander
Mariusz Chryc
PingWin
cvium
wehrstedt
BaronGreenback
David
martinek-stepan
Gary Wilber
Joshua M. Boniface
Fernando Fernández
Patrick Barron
Patrick Barron
Anthony Lavado
E.Smith
Mark Monteiro
telans