Account for 'NNN' like triplets RegexSearch store's translateSequence function.

CodonTable['NNN'] would return 'undefined', which would subsequently be
stringified into the translated sequence, causing incorrect calculation
of genomic coordinates for matched amino acid sequence. To address that
if lookup returns 'undefined', we use '?' instead.

Signed-off-by: Anurag Priyam <anurag08priyam@gmail.com>