(Hopefully) fix concurrency exceptions.

Emby.Server.Implementations/Session/SessionManager.cs

@@ -29,6 +29,7 @@ using MediaBrowser.Model.Library;
 using MediaBrowser.Model.Querying;
 using MediaBrowser.Model.Session;
 using MediaBrowser.Model.SyncPlay;
+using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
 using Episode = MediaBrowser.Controller.Entities.TV.Episode;
 
@@ -285,12 +286,19 @@ namespace Emby.Server.Implementations.Session
             if (user != null)
             {
                 var userLastActivityDate = user.LastActivityDate ?? DateTime.MinValue;
-                user.LastActivityDate = activityDate;
 
                 if ((activityDate - userLastActivityDate).TotalSeconds > 60)
                 {
+                    try
+                    {
+                        user.LastActivityDate = activityDate;
                         _userManager.UpdateUser(user);
                     }
+                    catch (DbUpdateConcurrencyException e)
+                    {
+                        _logger.LogWarning(e, "Error updating user's last activity date.");
+                    }
+                }
             }
 
             if ((activityDate - lastActivityDate).TotalSeconds > 10)