Some vessels generate multiple tweets

[ezod]

Occasionally, a vessel will generate multiple tweets (usually 2-3), with one "correct" photo and the others off-center or empty frame. The scheduler event is keyed by MMSI, and should be unique until 60 seconds after the tweet.

[ezod]

This seems to be a bug related to the non-scheduled capture and tweet for when the delta is less than half a second.

[2021-07-20 09:52:53.992198] SOME DEVIL: ship in view, tweeting...
[2021-07-20 09:52:55.696870] SOME DEVIL: image captured to /tmp/338189812.jpg
[2021-07-20 09:53:00.120939] SOME DEVIL: done tweeting
[2021-07-20 09:53:02.549867] SOME DEVIL: ship in view, tweeting...
[2021-07-20 09:53:04.269768] SOME DEVIL: image captured to /tmp/338189812.jpg
[2021-07-20 09:53:08.569030] SOME DEVIL: done tweeting
[2021-07-20 09:53:08.605714] SOME DEVIL: ship in view, tweeting...
[2021-07-20 09:53:10.292035] SOME DEVIL: image captured to /tmp/338189812.jpg
[2021-07-20 09:53:14.584837] SOME DEVIL: done tweeting

This may be triggering when AIS telemetry is received for vessels moving away from the camera axis which did not previously have a scheduled tweet.

[ezod]

Seems to be an issue in the event scheduler; the workaround in 872025f should be sufficient for now as long as the first scheduled shot is in the correct position.