Gui: Fix scroll behaviour in preference pages selector

This fixes problem with scroll jumping after selecting page on bottom of
the pages tree view. It was caused by collapsing group of the current
item and then re-expanding it few lines after.

Fixes: #12000

src/Gui/DlgPreferencesImp.cpp

@@ -56,6 +56,28 @@
 
 using namespace Gui::Dialog;
 
+bool isParentOf(const QModelIndex& parent, const QModelIndex& child)
+{
+    for (auto it = child; it.isValid(); it = it.parent()) {
+        if (it == parent) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+QModelIndex findRootIndex(const QModelIndex& index)
+{
+    auto root = index;
+
+    while (root.parent().isValid()) {
+        root = root.parent();
+    }
+
+    return root;
+}
+
 QWidget* PreferencesPageItem::getWidget() const
 {
     return _widget;
@@ -714,17 +736,6 @@ void DlgPreferencesImp::showEvent(QShowEvent* ev)
     }
 }
 
-QModelIndex findRootIndex(const QModelIndex& index)
-{
-    auto root = index;
-
-    while (root.parent().isValid()) {
-        root = root.parent();
-    }
-    
-    return root;
-}
-
 void DlgPreferencesImp::onPageSelected(const QModelIndex& index)
 {
     auto* currentItem = static_cast<PreferencesPageItem*>(_model.itemFromIndex(index));
@@ -790,14 +801,20 @@ void DlgPreferencesImp::onStackWidgetChange(int index)
         return;
     }
 
-    ui->groupsTreeView->selectionModel()->select(currentItem->index(), QItemSelectionModel::ClearAndSelect);
+    auto currentIndex = currentItem->index();
 
     auto root = _model.invisibleRootItem();
     for (int i = 0; i < root->rowCount(); i++) {
         auto currentGroup = static_cast<PreferencesPageItem*>(root->child(i));
+        auto currentGroupIndex = currentGroup->index();
+
+        // don't do anything to group of selected item
+        if (isParentOf(currentGroupIndex, currentIndex)) {
+            continue;
+        }
 
         if (!currentGroup->isExpanded()) {
-            ui->groupsTreeView->collapse(currentGroup->index());
+            ui->groupsTreeView->collapse(currentGroupIndex);
         }
     }
 
@@ -807,6 +824,8 @@ void DlgPreferencesImp::onStackWidgetChange(int index)
         ui->groupsTreeView->expand(parentItem->index());
         parentItem->setExpanded(wasExpanded);
     }
+    
+    ui->groupsTreeView->selectionModel()->select(currentIndex, QItemSelectionModel::ClearAndSelect);
 }
 
 void DlgPreferencesImp::changeEvent(QEvent *e)