[gui] active device deduction is not prevented when page is loaded on dashboard

The dashboard initialization that seems to appear once there are enough devices online… > the active devices calculation (should be resolved via MEN-4644) starts before the calls to receive the device number has returned (which takes slightly longer for large device counts). This prevents the device count cutoff for the active device calculation to not apply (yet). The result is way more load when you start off on the dashboard than landing on any other page.