Account correctly for the controller when computing wxBookCtrl best size.

Account correctly for the controller when computing wxBookCtrl best size.

We must not increase the total control size in the direction along the
controller window as the size of the controller in this direction is
determined by the size of the control itself. So doing this resulted in always
increasing best size in this direction to be at least equal to the current
size which was wrong.

Closes #14496.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72563 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775