fix nullpo when motdurl is null (#195)

* fix nullpo when motdurl is null

* prolly better

Author: ryo0ka

Essentials/EssentialsPlugin.cs

@@ -275,13 +275,10 @@ public void SendMotd(MyPlayer player, bool onSessionChanged)
         {
             long playerId = player.Identity.IdentityId;
 
-            var motdUrl = MyGuiSandbox.IsUrlWhitelisted(Config.MotdUrl)
-                ? Config.MotdUrl
-                : $"https://steamcommunity.com/linkfilter/?url={Config.MotdUrl}";
-            
             if (!string.IsNullOrEmpty(Config.MotdUrl) && !Config.NewUserMotdUrl)
             {
-                MyVisualScriptLogicProvider.OpenSteamOverlay(motdUrl, playerId);
+                var url = MakeUrl(Config.MotdUrl);
+                MyVisualScriptLogicProvider.OpenSteamOverlay(url, playerId);
                 return;
             }
 
@@ -298,7 +295,8 @@ public void SendMotd(MyPlayer player, bool onSessionChanged)
 
             if (!string.IsNullOrEmpty(Config.MotdUrl) && isNewUser && Config.NewUserMotdUrl)
             {
-                MyVisualScriptLogicProvider.OpenSteamOverlay(motdUrl, playerId);
+                var url = MakeUrl(Config.MotdUrl);
+                MyVisualScriptLogicProvider.OpenSteamOverlay(url, playerId);
                 return;
             }
 
@@ -324,6 +322,12 @@ public void SendMotd(MyPlayer player, bool onSessionChanged)
             }
         }
 
+        static string MakeUrl(string url)
+        {
+            if (MyGuiSandbox.IsUrlWhitelisted(url)) return url;
+            return $"https://steamcommunity.com/linkfilter/?url={url}";
+        }
+
         static string GetDefaultMotdText()
         {
             try