Fix Clear method (#614)

Make sure to clear the array before setting count to zero.

Source/MonoGame.Extended/Collections/Bag.cs

@@ -85,11 +85,11 @@ namespace MonoGame.Extended.Collections
             if(Count == 0)
                 return;
 
-            Count = 0;
-
             // non-primitive types are cleared so the garbage collector can release them
             if (!_isPrimitive)
                 Array.Clear(_items, 0, Count);
+
+            Count = 0;
         }
 
         public bool Contains(T element)
@@ -191,4 +191,4 @@ namespace MonoGame.Extended.Collections
             }
         }
     }
-}
+}