Fix adding images using local path

[Arlodotexe]

Background/Problem

Originally reported by @yoshiask in the Windows App Community #community-infra->Kermit coordination thread:

As an aside, I'm having issues with adding an image to a user:

.\WindowsAppCommunity.CommandLine.exe user images add --user-id k51qzi5uqu5dlcxnaakr3yg32iknb9lz8j0ydyglzldfkgge0otv9gyyy9douu --image-path "C:\Users\jjask\Pictures\Iskhyron.jpeg"
+118ms AddImageCommand InvokeAsync  [Information]  Getting modifiable entity
+314ms AddImageCommand InvokeAsync  [Information]  Got Id: k51qzi5uqu5dlcxnaakr3yg32iknb9lz8j0ydyglzldfkgge0otv9gyyy9douu
+314ms AddImageCommand InvokeAsync  [Information]  Input file:
+314ms AddImageCommand InvokeAsync  [Information]  - Id: C:\Users\jjask\Pictures\Iskhyron.jpeg
+315ms AddImageCommand InvokeAsync  [Information]    Name: Iskhyron.jpeg
+315ms AddImageCommand InvokeAsync  [Information]    GetType: OwlCore.Storage.System.IO.ContentAddressedSystemFile
Unhandled exception: System.InvalidOperationException: Source sequence doesn't contain any elements.
   at System.Linq.AsyncEnumerable.<FirstAsync>g__Core|88_0[TSource](IAsyncEnumerable`1 source, Func`2 predicate, CancellationToken cancellationToken) in /_/Ix.NET/Source/System.Linq.Async/System/Linq/Operators/First.cs:line 60
   at WindowsAppCommunity.CommandLine.Common.Images.AddImageCommand.InvokeAsync(String repo, String id, String imagePath, String imageId, String imageName) in C:\Users\jjask\source\repos\WindowsAppCommunity\WindowsAppCommunity.CommandLine\src\Commands\Common\Entity\Images\AddImageCommand.cs:line 60

Solution

Fix image retrieval logic in AddImageCommand to handle null imageId correctly.

[yoshiask]

Looks good to me, tested on my laptop