No Centroid Crashes the program

Hi there

Really interesting program. We noticed a bug when using your software, specifically there is an exception handling issue within the method update_centroid. When there is no centroid there is a value error which does not get handled in the current code. We did a workaround which can be found on my GitHub here.https://github.com/ScottGibb/idtrackerai/pull/1

If this is something you would like fixed, id be happy to contribute to a fix, but unsure how you want this to be handled, the fix we did was a quick workaround