Fix incorrect tabs selection handling when tab gets removed

#1843

Source/Editor/GUI/Tabs/Tab.cs

@@ -13,6 +13,8 @@ namespace FlaxEditor.GUI.Tabs
     [HideInEditor]
     public class Tab : ContainerControl
     {
+        internal Tabs _selectedInTabs;
+
         /// <summary>
         /// Gets or sets the text.
         /// </summary>
@@ -86,5 +88,25 @@ namespace FlaxEditor.GUI.Tabs
         {
             return new Tabs.TabHeader((Tabs)Parent, this);
         }
+
+        /// <inheritdoc />
+        protected override void OnParentChangedInternal()
+        {
+            if (_selectedInTabs != null)
+                _selectedInTabs.SelectedTab = null;
+
+            base.OnParentChangedInternal();
+        }
+
+        /// <inheritdoc />
+        public override void OnDestroy()
+        {
+            if (IsDisposing)
+                return;
+            if (_selectedInTabs != null)
+                _selectedInTabs.SelectedTab = null;
+
+            base.OnDestroy();
+        }
     }
 }

Source/Editor/GUI/Tabs/Tabs.cs

@@ -263,7 +263,12 @@ namespace FlaxEditor.GUI.Tabs
                 // Check if index will change
                 if (_selectedIndex != index)
                 {
-                    SelectedTab?.OnDeselected();
+                    var prev = SelectedTab;
+                    if (prev != null)
+                    {
+                        prev._selectedInTabs = null;
+                        prev.OnDeselected();
+                    }
                     _selectedIndex = index;
                     PerformLayout();
                     OnSelectedTabChanged();
@@ -342,8 +347,13 @@ namespace FlaxEditor.GUI.Tabs
         /// </summary>
         protected virtual void OnSelectedTabChanged()
         {
+            var selectedTab = SelectedTab;
             SelectedTabChanged?.Invoke(this);
-            SelectedTab?.OnSelected();
+            if (selectedTab != null)
+            {
+                selectedTab._selectedInTabs = this;
+                selectedTab.OnSelected();
+            }
         }
 
         /// <inheritdoc />