Fix crash that would occur when performing certain actions after removing all tabs (#4271)

* Ensure we can deselect notebooks

* Add changelog entry

* Use dynamic_cast instead of raw cast

CHANGELOG.md

@@ -8,6 +8,7 @@
 - Minor: Tables in settings window will now scroll to newly added rows. (#4216)
 - Minor: Added link to streamlink docs for easier user setup. (#4217)
 - Minor: Added setting to turn off rendering of reply context. (#4224)
+- Bugfix: Fixed crash that would occur when performing certain actions after removing all tabs. (#4271)
 - Bugfix: Fixed highlight sounds not reloading on change properly. (#4194)
 - Bugfix: Fixed CTRL + C not working in reply thread popups. (#4209)
 - Bugfix: Fixed message input showing as red after removing a message that was more than 500 characters. (#4204)

src/widgets/Notebook.cpp

@@ -156,16 +156,15 @@ int Notebook::indexOf(QWidget *page) const
 
 void Notebook::select(QWidget *page, bool focusPage)
 {
-    if (!page)
-    {
-        return;
-    }
-
     if (page == this->selectedPage_)
     {
+        // Nothing has changed
         return;
     }
 
+    if (page)
+    {
+        // A new page has been selected, mark it as selected & focus one of its splits
         auto *item = this->findItem(page);
         if (!item)
         {
@@ -196,9 +195,11 @@ void Notebook::select(QWidget *page, bool focusPage)
                 }
             }
         }
+    }
 
-    if (this->selectedPage_ != nullptr)
+    if (this->selectedPage_)
     {
+        // Hide the previously selected page
         this->selectedPage_->hide();
 
         auto *item = this->findItem(selectedPage_);
@@ -1169,22 +1170,29 @@ SplitContainer *SplitNotebook::getOrAddSelectedPage()
 {
     auto *selectedPage = this->getSelectedPage();
 
-    return selectedPage != nullptr ? (SplitContainer *)selectedPage
-                                   : this->addPage();
+    if (selectedPage)
+    {
+        return dynamic_cast<SplitContainer *>(selectedPage);
+    }
+
+    return this->addPage();
 }
 
 void SplitNotebook::select(QWidget *page, bool focusPage)
 {
-    if (auto selectedPage = this->getSelectedPage())
+    // If there's a previously selected page, go through its splits and
+    // update their "last read message" indicator
+    if (auto *selectedPage = this->getSelectedPage())
     {
-        if (auto splitContainer = dynamic_cast<SplitContainer *>(selectedPage))
+        if (auto *splitContainer = dynamic_cast<SplitContainer *>(selectedPage))
         {
-            for (auto split : splitContainer->getSplits())
+            for (auto *split : splitContainer->getSplits())
             {
                 split->updateLastReadMessage();
             }
         }
     }
+
     this->Notebook::select(page, focusPage);
 }