db: enforce tournament date only if it exists
db: enforce tournament date only if it exists

Tournament date can still be None if season
dates are None. So we have to prevent inter-ladder
match date check if tournament date is not set.

Signed-off-by: Ilija Hadzic <47a09d4a4430975766160361f65fc72633be50b6@gmail.com>

ihadzic/jim,ihadzic/jim,ihadzic/jim