If we don't wait here, we might end up running the subsequent commands (like
:command-history-prev) on the old window while it's still closing, causing an
exception at least on AppVeyor:
Traceback (most recent call last):
File "C:\projects\qutebrowser\qutebrowser\app.py", line 110, in <lambda>
target_arg=target_arg))
File "C:\projects\qutebrowser\qutebrowser\app.py", line 265, in process_pos_args
win_id = mainwindow.get_window(via_ipc, force_tab=True)
File "C:\projects\qutebrowser\qutebrowser\mainwindow\mainwindow.py", line 89, in get_window
window.setWindowState(window.windowState() & ~Qt.WindowMinimized)
RuntimeError: wrapped C/C++ object of type MainWindow has been deleted
407537dbe6