[do_jdbc] Make 0 time values return a Ruby nil
[do_jdbc] Make 0 time values return a Ruby nil

* This may not be the way to do it - but it makes the specs pass.

Signed-off-by: Alex Coles <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@alexcolesportfolio.com>

simonkro/do_mysql,simonkro/do_mysql,simonkro/do_mysql