cubicweb-timeseries #2532486 can't copy NonPeriodicTimeseries [done]

as it attemps to grok already interpreted data, leading to a crash

prioritynormal
typebug
done in1.3.1
load0.100
load left0.000
closed by#5ccda354ede6 check data isn't already interpreted in importer for non periodic timeseries, allowing them to be e.g. copied. Closes #2532486