blender crash - Win32 Error# (6): The handle is invalid.

[hannesdelbeke]

blender crashes when running

import bqt 
from bqt import hello_world
bqt.register()
bqt.instantiate_application()  # <== crash here

upon investigation it happens during the init of BlenderApplication()
blender crashes on this line in bqt/blender_applications/blender_application.py

self._blender_window = QWindow.fromWinId(self._hwnd)
self.blender_widget = QWidget.createWindowContainer(self._blender_window)  # crashes here

the error thrown is
Win32 Error# (6): The handle is invalid.

[hannesdelbeke]

turns out it crashes because we dont store the qt window.
so python garbage collects it as soon as the script ends
since blender is parented to this window, blender also closes.

fix to this is to save the variable in blender.
by running a startup script. bqt_startup.py (which is not yet in this repo, but is included in the pip package)