Set active = True after setting currentPlane to avoid race condition.

[wiseman]

Fixes a race condition in axis-ptz/camera.py.

The mqtt message handler was setting active = True before it set currentPlane, which meant that when the first message was received it would be possible for the camera thread to begin trying to process currentPlane when it was still None.

This probably isn't a race condition that would manifest often, but in my case I was sending the wrong JSON on the flight mqtt topic, which not only triggered the race but also was a bit extra confusing because the exception was being silently eaten (See PR #24).

[robotastic]

Great catch!
@wiseman I also have a fork that adds ONVIF support: https://github.com/robotastic/SkyScan
I will work on getting it merged in.

[wiseman]

Thanks for the link to the ONVIF fork, @robotastic—I was just starting on that.

[mchadwick-iqt]

Good find @wiseman, thanks for the contribution. We have an active issue where the axis-ptz container will stop working at a seemingly random interval (days to weeks). Going to investigate if this was part of what was happening. Any rare event will randomly occur given enough time.