Fixed: Can't login with a username and a blank password

Co-Authored-By: Mark McDowall <markus101@users.noreply.github.com>

src/Lidarr.Http/Authentication/AuthenticationModule.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using Nancy;
 using Nancy.Authentication.Forms;
 using Nancy.Extensions;
@@ -26,8 +26,7 @@ namespace Lidarr.Http.Authentication
         {
             Ensure.That(resource.Username, () => resource.Username).IsNotNullOrWhiteSpace();
 
-            // TODO: A null or empty password should not be allowed, uncomment in v3
+            Ensure.That(resource.Password, () => resource.Password).IsNotNullOrWhiteSpace();
-            //Ensure.That(resource.Password, () => resource.Password).IsNotNullOrWhiteSpace();
 
             var user = _userService.FindUser(resource.Username, resource.Password);