Values inside IN () restrictions may be either in a vector _in_values or
a marker (_in_marker or _value). To determine which one is appropriate
we check whether _in_values is empty, which is wrong because IN clause
can be empty (and there is no marker in such case). This is fixed by
using the presence of a marker to determine whether a vector of values
or a marker should be used.
Signed-off-by: Paweł Dziepak <pdziepak@cloudius-systems.com>
