Incorrect results for positional variable operator '#' on input arrays

[andrew-coleman]

The # operator introduced in v1.7.0 is not working as designed for input JSON with top-level arrays. For example, the expression $#$pos[$pos < 3] is saying 'bind the variable $pos to the position (index) of each value in the input array, then filter the results to contain only those with index less than 3'. When applied to the input array [3,1,4,1,5,9], it should return [3,1,4]. However, in v1.7.0, it is returning nothing. This expression is equivalent to the expression $[[0..2]], which returns the correct [3,1,4].