fix(jobs): fix wrong PK processing logic in genMultiplePartitionQuery funcs

[illia-li]

Us part of solution #354 (comment).
At this moment PK processig logic in genMultiplePartitionQuery funcs :

	for i, pk := range t.PartitionKeys {
		builder = builder.Where(qb.InTuple(pk.Name, numQueryPKs))
		for j := 0; j < numQueryPKs; j++ {
			vs := g.GetOld()
			if vs == nil {
				return nil
			}
			values = append(values, vs.Value[i])
			typs = append(typs, pk.Type)
	}

Which leads to generate stmt`s with failed PK values combinations and exhaust oldValues channels in generators.
As result or this PR - count of responses with nil rows decreased on 20%.