QMdiarea subwindow does not remember its last focus widget when adding new QMdiSubWindow

if a Subwindow in a QMdiaArea is created with few child input widgets it always assigns focus to first widget on activation after a new subwindow has been created.

Attached example reproduces this.

• Run the attached example qtbug38378.zip and click on "new subwindow" menu
• Note new subwindow has line edit #2 focussed
• Click on "new subwindow" again to create another subwindow
• Click on any line edit to give focus to that
• Now click on first subwindow's title bar to activate, you will see first line edit has the focus.