fixes #398 - Mb Web client - Release date metadata error

MediaBrowser.Api/ItemUpdateService.cs

@@ -222,8 +222,8 @@ namespace MediaBrowser.Api
             item.Studios = request.Studios.Select(x => x.Name).ToList();
             item.People = request.People.Select(x => new PersonInfo { Name = x.Name, Role = x.Role, Type = x.Type }).ToList();
 
-            item.EndDate = request.EndDate != default(DateTime) ? request.EndDate : null;
+            item.EndDate = request.EndDate.HasValue ? request.EndDate.Value.ToUniversalTime() : (DateTime?)null;
-            item.PremiereDate = request.PremiereDate != default(DateTime) ? request.PremiereDate : null;
+            item.PremiereDate = request.PremiereDate.HasValue ? request.PremiereDate.Value.ToUniversalTime() : (DateTime?)null;
             item.ProductionYear = request.ProductionYear;
             item.AspectRatio = request.AspectRatio;
             item.Language = request.Language;