Only use keyed fields in Index fetch

when filter clause includes a keyed and a non-keyed field, and an index fetch is performed, the non-keyed field is being used in the fetch condition causing an error.

for example:
select * from tutorial::rp::tutorialperson where zip = '54530' and middlename = 'N'

Index file '~tutorial::rp::peoplebyzipindex' is keyed by zip, but not by middlename.

Resulting ECL:

import std;
Tbl1RecDef := RECORD string15 firstname; string25 lastname; string15 middlename; string5 zip; string42 street; string20 city; string2 state; unsigned8 fpos

{virtual(fileposition)}

; END;
Tbl1DS := DATASET('~tutorial::rp::tutorialperson', Tbl1RecDef,FLAT);

Idx := INDEX(Tbl1DS,

{zip}

,

{ fpos }

,'~tutorial::rp::peoplebyzipindex');
IdxDS := FETCH(Tbl1DS, Idx( ( zip = '54530' )), RIGHT.fpos);

SelectStruct := RECORD
string15 middlename := IdxDS.middlename;
string5 zip := IdxDS.zip;
string20 city := IdxDS.city;
string2 state := IdxDS.state;
string15 firstname := IdxDS.firstname;
string42 street := IdxDS.street;
string25 lastname := IdxDS.lastname;
END;
IdxDSTable := TABLE(IdxDS, SelectStruct );
OUTPUT(CHOOSEN(IdxDSTable,ALL),NAMED('JDBCSelectQueryResult'));

Total elapsed http request/response time in milliseconds: 189
Parsing results...
java.sql.SQLException: java.lang.Exception: HPCCJDBC: Error in response: ' Unknown identifier "middlename"'