We allow opening new windows as a fallback in case the app doesn't give
us explicit information about it, but we don't want to allow opening new
windows if we're unable to ask for this information (we can only use the
APIs to get this information while the app is RUNNING).
So always return FALSE in case the app is STARTING, always return TRUE
in case the app is STOPPED (starting an app always opens a new window)
and go through the usual checks in case the app is RUNNING (and
eventually fall back to FALSE).
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/121
00e95de114