Fix do_after throwing on attaching to new entity (#1679)

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Client/GameObjects/EntitySystems/DoAfter/DoAfterGui.cs

@@ -43,6 +43,25 @@ namespace Content.Client.GameObjects.EntitySystems.DoAfter
             LayoutContainer.SetGrowVertical(this, LayoutContainer.GrowDirection.Begin);
         }
 
+        /// <summary>
+        ///     Called when the mind is detached from an entity
+        /// </summary>
+        ///     Rather than just dispose of the Gui we'll just remove its child controls and re-use the control.
+        public void Detached()
+        {
+            foreach (var (_, control) in _doAfterControls)
+            {
+                control.Dispose();
+            }
+            _doAfterControls.Clear();
+            foreach (var (_, control) in _doAfterBars)
+            {
+                control.Dispose();
+            }
+            _doAfterBars.Clear();
+            _cancelledDoAfters.Clear();
+        }
+
         /// <summary>
         ///     Add the necessary control for a DoAfter progress bar.
         /// </summary>

Content.Client/GameObjects/EntitySystems/DoAfter/DoAfterSystem.cs

@@ -57,7 +57,7 @@ namespace Content.Client.GameObjects.EntitySystems.DoAfter
         {
             _player = entity;
             // Setup the GUI and pass the new data to it if applicable.
-            Gui?.Dispose();
+            Gui?.Detached();
 
             if (entity == null)
             {