appview/pulls: handle deleted forks in branch status check

Signed-off-by: oppiliappan <[e-mail]>

appview/pulls/pulls.go

···
 		return nil
 	}
 
+	// deleted fork
+	if repo == nil {
+		return nil
+	}
+
 	// user can only delete branch if they are a collaborator in the repo that the branch belongs to
 	perms := s.enforcer.GetPermissionsInRepo(user.Did, repo.Knot, repo.DidSlashRepo())
 	if !slices.Contains(perms, "repo:push") {