BIND with type errors result leads to cross joins instead of empty result

[abrokenjester]

(Migrated from https://openrdf.atlassian.net/browse/SES-2250 )

When using a BIND variable in a pattern join, the result is a cross join of the dataset triple when the BIND expression raises a type error.

This query should expose the behavior on any store that contains blank nodes.
{code}
SELECT *
WHERE {
?s ?p ?o .
FILTER(isBlank(?o))
BIND (iri(?o) as ?s2)
?s2 ?p2 ?o2 .
} LIMIT 10
{code}

The join evaluation should normally conclude that both multisets are incompatible since ?s2 is unbound in the join's left argument so the query should normally return no result.

[catch-point]

To fix this we need to introduce a binding state that causes the variable to remain unbound in the solution. The spec says If the evaluation of the expression produces an error, the variable remains unbound for that solution but the query evaluation continues.