cubicweb #1965481 [facet] add safety belt to rqlpathfacet [resolved]

when filter_variable == label_variable

this would avoid a painful debugging session

prioritynormal
typebug
done in3.13.7
load0.200
load left0.000
closed by#be04706eacc9 [facet] add safety belt to rql path facet init (closes #1965481)