Fix null ref when no remote branch

This issue was introduced in #1248.

Author: jcansdale

src/GitHub.Exports/Models/BranchModel.cs

@@ -31,9 +31,8 @@ public BranchModel(LibGit2Sharp.Branch branch, IRepositoryModel repo)
             Extensions.Guard.ArgumentNotNull(repo, nameof(repo));
             Name = DisplayName = branch.FriendlyName;
 #pragma warning disable 0618 // TODO: Replace `Branch.Remote` with `Repository.Network.Remotes[branch.RemoteName]`.
-            var remoteUrl = branch.Remote.Url;
+            Repository = branch.IsRemote ? new LocalRepositoryModel(branch.Remote.Url) : repo;
 #pragma warning restore 0618
-            Repository = branch.IsRemote ? new LocalRepositoryModel(remoteUrl) : repo;
             IsTracking = branch.IsTracking;
             Id = String.Format(CultureInfo.InvariantCulture, "{0}/{1}", Repository.Owner, Name);
         }