Fix some resharper warnings and errors

PartyModes/PartyModeChallengeMedley/CPartyModeChallengeMedley.cs

@@ -18,6 +18,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Linq;
 using System.Runtime.InteropServices;
 using VocaluxeLib.Game;
 using VocaluxeLib.Menu;
@@ -386,9 +387,7 @@ namespace VocaluxeLib.PartyModes.ChallengeMedley
             }
 
             //Calc avarage sing-count
-            int totalCounts = 0;
-            foreach (CSong song in visibleSongs)
-                totalCounts += song.NumPlayedSession;
+            int totalCounts = visibleSongs.Sum(song => song.NumPlayedSession);
             int averageCount = totalCounts / visibleSongs.Count;
 
             // ReSharper disable LoopCanBeConvertedToQuery