Fix all warnings from the cppcoreguidelines-pro-type-member-init clang-tidy check (#4426)

src/widgets/settingspages/AboutPage.hpp

@@ -16,7 +16,7 @@ private:
     void addLicense(QFormLayout *form, const QString &name_,
                     const QString &website, const QString &licenseLink);
 
-    QLabel *logo_;
+    QLabel *logo_{};
 };
 
 }  // namespace chatterino

src/widgets/settingspages/AccountsPage.hpp

@@ -14,9 +14,9 @@ public:
     AccountsPage();
 
 private:
-    QPushButton *addButton_;
-    QPushButton *removeButton_;
-    AccountSwitchWidget *accountSwitchWidget_;
+    QPushButton *addButton_{};
+    QPushButton *removeButton_{};
+    AccountSwitchWidget *accountSwitchWidget_{};
 };
 
 }  // namespace chatterino

src/widgets/settingspages/SettingsPage.hpp

@@ -85,7 +85,7 @@ public:
     }
 
 protected:
-    SettingsDialogTab *tab_;
+    SettingsDialogTab *tab_{};
     pajlada::Signals::NoArgSignal onCancel_;
     pajlada::Signals::SignalHolder managedConnections_;
 };