Mowing detection date conversion

[davidfrantz]

There seems to be a bug in the mowing detection python UDF that can cause no output when a date too early in the season is included:
davidfrantz/force#318 (reply in thread)

Apparently, the workaround is to use the DOY_RANGE parameters to mitigate this, but a proper fix might be the better solution.

[davidfrantz]

@geo-masc
@ernstste

can you help here?

[geo-masc]

@davidfrantz I just saw the discussion. Thanks @ernstste for clarifying. We had the same issue for processing some tiles in Switzerland. I had in mind that we already pushed a solution. I will have a look at it.