yams #202008 [schema2dot] do not crash on symmetric relation [validation pending]

prioritynormal
typebug
done in0.39.1
load0.100
load left0.000
closed by#71f4cf1ec8bd [schema2dot] handle specialization 'none' relations (closes #202008)
patch[schema2dot] handle specialization 'none' relations (closes #202008) [applied]