Prevent dangling pointer

GUI/GraphicalUserInterface.cpp

@@ -636,11 +636,11 @@ namespace GraphicalUserInterface
 
     GUI::~GUI()
     {
-        delete this->mem;
-        delete this->BackBuffer;
-        delete this->DesktopBuffer;
-        delete this->OverlayBuffer;
-        delete this->CursorBuffer;
+        delete this->mem, this->mem = nullptr;
+        delete this->BackBuffer, this->BackBuffer = nullptr;
+        delete this->DesktopBuffer, this->DesktopBuffer = nullptr;
+        delete this->OverlayBuffer, this->OverlayBuffer = nullptr;
+        delete this->CursorBuffer, this->CursorBuffer = nullptr;
         Display->DeleteBuffer(200);
         for (size_t i = 0; i < this->Windows.size(); i++)
             this->Windows.remove(i);

GUI/WidgetEvents.cpp

@@ -57,7 +57,8 @@ namespace GraphicalUserInterface
             LastHeight = ((Window *)this->ParentWindow)->GetPosition().Height;
 
             this->mem->FreePages(this->Buffer->Data, TO_PAGES(this->Buffer->Size));
-            delete this->Buffer;
+            this->Buffer->Data = nullptr;
+            delete this->Buffer, this->Buffer = nullptr;
 
             this->Buffer = new ScreenBitmap;
             this->Buffer->Width = LastWidth;

GUI/Widgets.cpp

@@ -117,8 +117,8 @@ namespace GraphicalUserInterface
 
     WidgetCollection::~WidgetCollection()
     {
-        delete this->mem;
-        delete this->Buffer;
-        delete this->CurrentFont;
+        delete this->mem, this->mem = nullptr;
+        delete this->Buffer, this->Buffer = nullptr;
+        delete this->CurrentFont, this->CurrentFont = nullptr;
     }
 }

GUI/Window.cpp

@@ -60,6 +60,6 @@ namespace GraphicalUserInterface
 
     Window::~Window()
     {
-        delete this->mem;
+        delete this->mem, this->mem = nullptr;
     }
 }

GUI/WindowEvents.cpp

@@ -15,7 +15,8 @@ namespace GraphicalUserInterface
     {
         // TODO: Optimize this
         this->mem->FreePages(this->Buffer->Data, TO_PAGES(this->Buffer->Size));
-        delete this->Buffer;
+        this->Buffer->Data = nullptr;
+        delete this->Buffer, this->Buffer = nullptr;
 
         this->Buffer = new ScreenBitmap;
         this->Buffer->Width = e->Resize.Width;