cubicweb #2818280 ignore looping tasks with a negative interval instead of crashing [validation pending]

using a negative value for looping task interval would be a convenient way of disabling it. Also there's no reason to reject interval=0.

prioritynormal
typeenhancement
done in3.17.0
load0.250
load left0.000
closed by#da2007002dca [task] allow negative intervals for add_looping_task (closes #2818280)
patch[task] allow negative intervals for add_looping_task (closes #2818280) [applied]allow negative intervals for add_looping_task (closes #2818280) [applied]