nazca #235720 fix non return value of _sparqlexecute [validation pending]

if _sparqlexecute return no result we should not try to access this result

prioritynormal
typebug
done in0.5.1
load0.100
load left0.000
closed by#aed668ce06ea [sparql] handle empty result of _sparqlexecute (closes #235720)
patch[sparql] handle empty result of _sparqlexecute (closes #235720) [applied]