promise: Support sites w/o certificate in check_surykatka_json

Sites with bad certificates are reported with null values in surykatka
output, thus they have to be handled correctly.
4 jobs for feature/surykatka-elapsed-time in 0 seconds
Status Job ID Name Coverage
  External
failed SlapOS.Eggs.UnitTest-luke.Python2

00:25:19

failed SlapOS.Eggs.UnitTest-luke.Python3

00:24:37

failed SlapOS.Eggs.UnitTest-luke.Python2

00:10:36

failed SlapOS.Eggs.UnitTest-luke.Python3

00:21:34