Still resize wxSplitterWindow children even when sash position doesn't change.

Still resize wxSplitterWindow children even when sash position doesn't change.

Since the changes if r68876, the splitter windows were not resized correctly
if the splitter size in the direction orthogonal to its own didn't change.
This was an unintended side effect of the changes in that commit as it only
wanted to avoid calling SetSashPositionAndNotify() in this case, but
SizeWindows() should still be called.

Ensure that we do call it always from wxSplitterWindow::OnSize() to fix this.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69059 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775