Log instead of just crashing when `PostLogoutRedirectUris` in client definition is empty

https://github.com/dotnet/aspnetcore/blob/6f4860eaa8f5281eb4fbabbe830f0c28254d3087/src/Identity/ApiAuthorization.IdentityServer/src/Extensions/DefaultClientRequestParametersProvider.cs#L49-L57

When the client definition has no post logout redirect uris defined, line 54 simply throws without any indication in the log of what the issue was.

It would be beneficial to developers if a log message would be shown to explain the exception.

Alternatively, provide some default value in case the list is empty such as the root path `/`.