A bunch of tab fixes (#6551)

* Make sure the speed tab is properly hidden when toggle off advance mode

* Clear each page before clearing the parent, otherwise the child pages will be destroyed twice

* Fix crash if current selected tab is positioned after the removed tab

* Fix issue that sometimes the printer config first page is not displayed

* Fix issue that the wrong tab item get bold if the number of tabs changed

src/slic3r/GUI/Widgets/TabCtrl.cpp

@@ -120,6 +120,11 @@ bool TabCtrl::DeleteItem(int item)
     if (item < 0 || item >= btns.size()) {
         return false;
     }
+    const bool selection_changed = sel >= item;
+
+    if (selection_changed) {
+        sendTabCtrlEvent(true);
+    }
 
     Button* btn = btns[item];
     btn->Destroy();
@@ -127,9 +132,12 @@ bool TabCtrl::DeleteItem(int item)
     sizer->Remove(item * 2);
     if (btns.size() > 1)
         sizer->GetItem(sizer->GetItemCount() - 1)->SetMinSize({0, 0});
+
+    if (selection_changed) {
+        sel--;  // `relayout()` uses `sel` so we need to update this before calling `relayout()`
+    }
     relayout();
-    if (sel >= item) {
-        sel--;
+    if (selection_changed) {
         sendTabCtrlEvent();
     }