Come on.
A jar standing on its own in a room, versus one secured in a storage area. It's secured well, in place for long journeys?
The movie showed no leakage. Ergo, It was obviously secured in such a manner as to prevent spills. This is far less far fetched than super fridge and his sidekick, Terminator Jones.
EDIT: Unless, of course, there was another entrance, in which case there could have been a leak, but the room was sealed and therefore the problem was moot. Either way, it didn't play a factor.