Crash/inifinite loop when tabbing dock widget

In some cases you can have an infinite loop.
In KWord, you can run it and then try to tab a dock widget and it will trigger the problem.
The special thing to reproduce this is to connect to the visibilityChanged signal of the dock widget and then saving the state of the main window.

The problem is that when we change the current tab in the tabbar, the layout is still in an intermediate state. So we need to make sure it is in a valid state before setting the current tab.