Allow mind transfer to entity if said entity is also the current visit target.

Content.Server/Mobs/Mind.cs

@@ -1,7 +1,8 @@
-using System;
+using System;
 using System.Collections.Generic;
 using Content.Server.GameObjects.Components.Mobs;
 using Content.Server.Players;
+using Robust.Server.Interfaces.GameObjects;
 using Robust.Server.Interfaces.Player;
 using Robust.Shared.Interfaces.GameObjects;
 using Robust.Shared.IoC;
@@ -142,6 +143,7 @@ namespace Content.Server.Mobs
         public void TransferTo(IEntity entity)
         {
             MindComponent component = null;
+            bool alreadyAttached = false;
             if (entity != null)
             {
                 if (!entity.TryGetComponent(out component))
@@ -153,6 +155,17 @@ namespace Content.Server.Mobs
                     // TODO: Kick them out, maybe?
                     throw new ArgumentException("That entity already has a mind.", nameof(entity));
                 }
+
+                if (entity.TryGetComponent(out IActorComponent actor))
+                {
+                    // Happens when transferring to your currently visited entity.
+                    if (actor.playerSession != Session)
+                    {
+                        throw new ArgumentException("Visit target already has a session.", nameof(entity));
+                    }
+
+                    alreadyAttached = true;
+                }
             }
 
             OwnedMob?.InternalEjectMind();
@@ -160,7 +173,7 @@ namespace Content.Server.Mobs
             OwnedMob?.InternalAssignMind(this);
 
             // Player is CURRENTLY connected.
-            if (Session != null && OwnedMob != null)
+            if (Session != null && OwnedMob != null && !alreadyAttached)
             {
                 Session.AttachToEntity(entity);
             }