TabWidget::currentChanged(int index) can be emited with index == -1,
which means there are no tabs in tabbar. This may lead to crash after
accessing current webview (null)
Set of patches:
Introduce TabStackedWidget+ComboTabbar
[Windows] Fix enabling blur background in fullscreen
[ComboTabBar] Fix some issues with pinned tabs
[ComboTabBar] Don't use pointer to integer,
Implement TabStackedWidget::keyPressEvent() and fix changing tab by wheel event
Fix animation delay of dragged tab's buttons.
[ComboTabBar] Add themable scrollButtons