Dirk fix rain nodata  null instead of 0  client

Problem
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Client can not distinguish between "no data available" and "zero rain has fallen" in the rain graph (card, not timeline) after clicking on the map.

Solution
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Only show the card if data returned from the raster service contains at least one other value than null/None.

x-reference: https://github.com/nens/lizard-nxt/pull/308