Replace array:to_list(array:new()) with lists:duplicate

Perhaps there was a performance reason for doing
array:to_list(array:new(length(FieldNames))), but in my non-scientific
benchmarks, it appeared to mostly (but only marginally) faster to use
lists:duplicate, and frankly, I think it's a little clearer what's going
on with lists:duplicate, since it's a single function call rather than
having to know that a new empty array of size X will return a list of X
undefined atoms from array:to_list.